Haven't been involved with Jango for awhile and realize this thread is old... so refresh me if I am wrong, but is it not reasonable to assume that Jango Fett owned multiple jet packs before the arena scene? Was is officially stated that the arena pack came later?
Still seems a bit of a reach to me, and definitely something only enthusiasts would quarrel over. Have to ask yourself what is most important to you. Personally, I'd leave the costume as YOU enjoy it...but I certainly understand wanting to participate.