Streamlining everything that's been put out so far...
-Conflicting stories in the EU as to the origin of Boba's "dent" (really a crater), and how many he has
-Conflicting opinions as to when Jango's helmet acquires its dent
-EU fluff being treated as the same as explicit film canon as far as armor properties (beskar and all that)
See what I can do to concisely bash things into clear order...
Going by real-world chronology, Boba came first. Allowing for swap-out-able accessories (gauntles, pack, cape, etc.) his armor and helmet in ROTJ were intended to be the same as the armor and helmet he had in ESB. Lucasfilm Archives folks have proven several times that they can't spot the minute differences fan costumers have spotted over the years. Indeed, Lucasfilm sent the Pre-Pro 3 helmet to Master Replicas, thinking it was the ESB Hero, and refused to belive/accept they'd been mistaken when the expert MR called in to create a master for the paint apps pointed out the error. The damage and paint apps are too similar for mere coincidence to allow for the same stuff to happen in the same places.
Remember all three original films were out before home video had really fully exploded as a thing. That was still an era when filmmakers took shortcuts and had a "enh, whatever" attitude toward continuity of minutiae. Frame-flops, differences in costumes/props/sets/models/whatever were never expected to receive repeated close scrutiny. People would see it in the theater one, twice, a dozen times, and done and gone.
Later, from the novels and comics, we have no less than three separate stories of Boba's escape from the Sarlacc. One of those ended with him going back in, so one of the others could be considered to follow onto that story, but that guy has seriously got the worst luck. The EU has also given us multiple and conflicting stories as to the origin of the crater in his helmet. I'll draw attention to what's been said before, at the risk of bringing real-world stuff into it. My Mando armor is 16-gauge stainless steel. One of the chest plates accidentally got backed over in the driveway. As in, by a car. It wasn't bent, dented, scraped, ruined, or mussed in any way. I'll deal with beskar and the "duraseel is ****" stuff that got added later on in a bit. Point is, it takes a lot of concentrated, directed force to bash out an impact crater like that. There are only two possibilities that wouldn't have resulted in a broken neck for the wearer: 1) it wasn't being worn at the time; 2) It's some kind of active ablative armor, and some of the incoming kineic energy was dissipated/redirected outward in lost material, while the thinner remaining material deformed inward.
As stated before, also, the costumers for AOTC had full access to all of the Boba stuff in the archives, includeing no less than six helmets all with identical dents in identical places. If they wanted Jango's armor to be (or, rather, eventually become) Boba's, they would have made the collar and back plate overlap and lock together, rather than gap by an inch. They would have made the groin armor go all the way out to the sides and lock together with the "butt plate". They would have made the knees and gauntlets the same. And, most damning, Tem Morrison is 5'7". Alan Harris was, what, 6'2" at the time he test-fitted the armor? And Jeremy Bulloch was 6'1" when he wore it in the movies. Jango's helmet is noticeably smaller side-by-side with Boba's, symmetry issues aside. The cheekbones are also different shapes. And on and on.
We got several new EU sources telling conflicting stories after AOTC of what Boba did with his father's body, armor, and helmet. Anyone who's done metal armor knows it's far easier to just make a new set of plates than go to the trouble of resizing existing ones. The outlines won't necessarily match, let alone any mounts, sensors, padding, internal systems, etc. Plus, Mandalorians have a reputation of being a practical people -- I doubt Boba would ruin his dad's armor by making it small enough for him to wear... for a few months until he outgrew it. Then what? As for the helmet... Even if Boba hadn't done blowed it up to try to kill Mace, they are so heavily personalized for the wearer, it's just simpler to get one of your own set up for
your own preferences and eyeline and whatnot. Notice, in the EU, whatever else is done with the body and the armor, the grave marker is, wait for it, the Mando's helmet. Left to gather bird poop and mud.
Now, cultural in-universe timeline.
The Clone Wars has given us Mandalore and its "moon" Concordia. Last I checked, if a mon had the same mass and gravity and atmospheric density as its primary, it's not a moon. They're co-orbiting trojan planets. Concordia sure seems a lot like the Mandalore we see in the comics and novels set later on. The "Mandalore" we saw in the series is a good match for a desert planet in the system shown in the Atlas named Kalevala. My massaging of things to make it all fit is that some thousands of years ago, the Taung found these trojan planets with the catalogue names of Kalevala and Concordia and they settled them. After the events chronicled in KOTOR and TOR, he Republic smacked the Mandalorians down hard, turning their primarily-settled world, called Mandalore, into a desert.
This would have been the birth of the New Mandalorians, and it would have been an ongoing point of contention for centuries. By about 50-60BBY, the New Mandalorians had gained the ascendancy and outlawed the wearing of the armor. Out on Concord Dawn, the chief of the Protectors tried to enforce this and was killed by his subordinate, Jaster Mereel, for not being a true Mandalorian. He rallied others who felt the same to his cause and it was shaping up to be a coup of the New Mandalorians back on Kalevala-Mandalore until more conquest-minded True Mandalorians split off and formed the Death Watch. They fought. One of Jaster's old comrades who
had toed the party line and shelved his armor gave Jaster sanctuary. The Death Watch killed him and his wife and took his daughter. His son helped Jaster escpae, and was adopted by Jaster. That's Jaster Mereel's family crest on Boba's right chest plate.
That kid was Jango. The last Mandalore we know of for sure was Mandalore the Uniter, who was ambushed and murdered around 100BBY. I haven't seen anything that says Jaster or Jango claimed the title, even if they were acting as such. And, while the mask of the Mandalore had been passed from one to the next in antiquity, that tradition was broken long before this time.
By the time we get to the Clone Wars years later, the Death Watch has been quietly rebuilding on Concordia, for much of this time a sparsely-populated world mostly just used for mining. Something seems to have happened to Kalevala by the time the Empire had annexed the system, as we don't see it at all, and Concordia is now recognized as the planet Mandalore, now being strip-mined by the Empire. This is the world we still see decades later in the Legacyof the Force books.
Meanwhile, in between there, after the Clone Wars, Boba had gone back to the Mandalore Sector and tried to have a normal life as a Protector on Concord Dawn, himself. Got married, had a daughter. That lasted about three years --
but that's where we first see him having his own armor and the dented helmet.
The stories of him getting the dent from Vader or one of the Emperor's Guards' force pike butt or whatever are either misinformation put out there by Boba himself or stories told about him in hushed tones around blazing garbage bins in back alleys wherever hardened spacers gather to swap tales of terror. *heh*
All this --
all. this. -- to point out we still don't know where Boba first got his famous dent, that even if he has multiple backup armor pieces, he wore but one helmet in ESB and ROTJ (despite the folks at Lucasflm either not knowing or not caring if they grabbed the right helmet/armor), the helmet survived the sarlacc and he wore it for decades further until finally being browbeaten into accepting a new one in the Legacy of the Force books, and that none of that is what we saw Jango wearing in AOTC.
Deal with it.
--Jonah