After the patch...

[MorgothNL]

Hey,

the progress towards unlocking does not get set back to 0.
In your example, you will have unlocked the spit XVI, after you won killed 1 more plane with a spit.

this is what a dev said:
No, counters will not be reseted, but you have to get one more win/kill to achieve unlock.
(If you have 45 wins with a bomber, unlock the b-17 would be yours if you get the 46th win after title update)

hope you get it