I upgraded to "large meetings". Does the change affect meetings created before the upgrade?

Hi, @alex_fips.

The number of attendees permitted in a meeting is checked by Zoom during the process of opening the meeting.  So any Large Meeting add-on, or transfer over to someone else's account, or anything at all that would affect the meeting... nothing matters til you hit the Start or Join button.  You should be good to go as-is.