There are several flavors of "affordable" or "low income" lottery apartments. How long they are rent regulated falls to what program they were created under and what rules applied at that time. Generally units are RS until tax abatement period expires. By law leases are supposed to inform tenants if their building received tax abatement, when it will end, and what that means for rent regulated units.
https://hcr.ny.gov/system/files/docu...he%20apartment.
421-A used to be something like 25 years, but then it was changed to 35 or maybe a bit longer under BdeB.
Then you have units that are "permanently" affordable (something new, also from BdeB's time), meaning units never come out of RS long as that scheme exists.
STPCV is whole other ball of wax:
https://www.ibo.nyc.ny.us/iboreports...ct%20of%202015.
As to what happens when tax abatement ends, generally by law current tenant is protected and unit remains under that scheme until vacated. Once that happens any new tenant would be market rate.
This all presumes there will not be any changes to 2019 rent laws such as reinstatement of luxury decontrol.