locked jobs for cured villagers

i have cured some zombies villagers before and changed their profession perfectly fine. A couple (IRL) days later cured another zombie villager, and he had a profession from the start. i thought that was weird cause they're always nitwits from the start, so put a cartography table next to him to change him. Nothing happened. I tried with another newly cured villager with a different profession block and the same thing.