Hi
jhfagan ,
I am way deeper into in-universe lore / stuff then I am into real world costumes / details / ... .
That said, my knowledge is almost exclusively of pre-disney canon, as what disney has done with Star Wars (except the Mandalorian) has absolutely suffocated any interest in "modern" Star Wars that I may have had in the beginning. So as mentioned, except for the Mandalorian, what is now known as Legends is what I am into and with what I will stick. So all my info regarding your questions is exclusively Legends-sourced.
Now to your question... There are 2 parts to a proper answer.
1)
As far as I am aware, there has never been an in-universe explenation for the differences in Bobas apparence. This is in my eyes mainly due to it not being of any significance story-wise, just like the difference in Anakins / Lukes Lightsaber etc. Also, while it would be possible to find a meaningful explenation for that there are 2 versions of the armor at different points in in-universe time (which could be that there are 2 versions of the suit that he picks from as he sees fit), it would be impossible to find an explenation that makes sense to the RotJ / RotJ SE swaps in a matter of in-universe minutes in Jabbas palace. So there is that. Not picked up on by the expaned universe.
There is more inconsitencies and inexplicable things though!
Jangos armor is supposed to be Durasteel, not beskar. At least thats what it states in Wookiepedia. This would make zero sense. There are a lot of worse-off Mandos then he is who have real Beskar armor (Legends,... again...) and Jango even was THE Mandalore. So it makes no sense him having no real beskar armor.
The dented version of his helmet though shows, that it really could not have been real beskar as that doesnt dent.
2)
Now regarding how Fetts "wardrobe" looked like and how it developed, lets look at what he used in different periods of time in his life. Again... All Legends.
He started out using his dads helmet after Jango got killed. Later on, he grew into being able to use his armor, too. By the time of the original Trilogy, however, he used an entirely different set of armor made from duraplast (a white sort of metal).
Much later, waaay after Episode 6, he had (somehow inexplicably) downgraded to a set made out of durasteel. Actually, Skirata Clan Member Jaing Skirata joked to Fetts granddaughter Mirta Gev once, that when Fett dies and they part out his armor, she should watch out to get the flamethrower and no parts of his armor, since thats junk.
By then, Boba has become the Mandalore, although for a long time he has done a very very bad job in that position. After he came back to Mandalore (the planet) and associated more with his people, a Mandalorian smith named Medrit Vasur made him a new armor out of beskar, that also included a sort of neck-ring to avoid decapitation.
He also joked, that while painting it they could incorporate fake-patina for Boba to be able to keep his meanicing apparence. I am sure,
superjedi would have come in handy there
Ok, thats it.
Now a quick word about beskar.
In Legends, Beskar worked somewhat differently from how it is depicted in The Mandalorian. Yes, it was a very rare ore (native to Mandalore, the planet), but that was only part of where it got its superiour properties from. Because a lot of that also came from the smithing skills of the Mandalorian people. Kinda comparable to how Damaszener Steel is made in the real world: folding, hammering, folding hammering, and so on, creating a nice visual apparence while you are at it
Honestly, I dont really like how they chose to implement beskar into the Disney series... Just melting it down and half-heartedly hitting it with a hammer... meh.... Seems so... supermarket-esque.
