That and the equations are exactly what I thought about in terms of "LOOK HE GOT OLDER". Five just thinks he got the equations right and maybe he did. Maybe he did't. But he can also slip through time a bit more easily. Maybe tries to work on "fixing" his body or it's otherwise waved off as him messing around to learn more. In the process he's like, "Well, guess who's functionally immortal! No, not you, Klaus. Shut up." Bing bang boom it's all done.
But agreed. This isn't something they can't have thought about knowing that, if nothing else, the comics are going to be 8 volumes long, so Netflix is likely to greenlight more than one or two seasons. They already planted the "I'll give you the right math" thing. So it's there. In their minds.