I get that it's easy to cheat on homework, but tests can be more locked-down. Is it possible to retroactively ding a homework grade if subsequent testing shows

I get that it's easy to cheat on homework, but tests can be more locked-down. Is it possible to retroactively ding a homework grade if subsequent testing shows that the student truly does not know how to do the concept from the homework? Obviously we all forget things over time, but if the homework was suspect from the beginning, and when the student is tested he has just no idea whatsoever, that could be grounds for taking back some of the homework credit.