Currently, the M1A2 SEP is in a folded state, requiring only 200,000 research points to develop. The next version, M1A2 SEP, will require 400,000 research points. I’ve already completed the research, but I don’t have enough Silver Lions to purchase it.

Will the update still show the “research completed but not purchased” status?
(I’m worried that Gaijin will make me farm another 200,000 research points.)
You should be fine, but if you are that worried, you should get to grinding SL
Pretty sure like 99.9% that once you research a vehicle that’s it. You won’t get it locked or something.
I still have a researched F4U corsair in the US tree that I researched like 10 years ago and never bought and it’s now locked behind 4 unresearched planes and stuck in a rank I need 5 more planes to unlock. Yet the plane is still researched I just cannot buy it.
it shouldnt change except maybe SL cost, once its researched its researched