Is the attendee cap a cap of the total attendees in a month, total attendees in a given meeting, or total attendees for the plan?
The cap is on the total unique attendees for each meeting. After you end a meeting, the attendee count resets and you can give the meeting to another set of attendees (up to the attendee cap as shown here).
To see the attendee cap, navigate to the attendee list. You can get to the attendee list by either click the "user" icon in the upper right hand corner of Presenter view, or by going to Settings > Attendees > Attendee List.
In the Attendee List, you can see how many attendees are online, how many have joined the meeting, and your meeting cap displayed at the top of the list.
The attendee limit applies per meeting, not cumulatively across all meetings. For instance, with a 75-attendee limit, you can invite 75 participants to one meeting, conclude it, and then start a new meeting with a different link for another group of 75 attendees. This means you could have 150 unique participants across two meetings. The limit counts everyone who accessed the meeting, not just those currently present. Starting a new meeting resets the counter.
If you get more than 25 attendees on the free account, late attendees will not be able to access the meeting.