No, it isn't "ok". Those "reserve of votes" are the ones they create after they know how many they need. That's why they end up being all dem votes at the end.
When you stuff ballots you want to keep a ratio of about 70:30 - that way it draws less suspicion. What you do is isolate those ballots then when no one is watching count them again a few times... that is what was going on in Atlanta in that much talked about video from 2020.