Can I upload more email addresses than my webinar license is designed for?

Welcome to the Zoom Community, @JulieBW.

You can certainly over-register your webinar.  The limitation is on how many people are permitted to join/attend.  Most webinars see attendance in the 50-60% of registrants range.  If you think there's a possibility that you'll have more attendees than you are currently licensed for, you have a few options:

1. Wait and see... maybe you won't reach the limit.
2. Create a Live-Stream to YouTube or other service, and let people know that if they arrive late and the audience is at capacity, and to head on over to (insert live-stream URL here).
3. Consider upgrading your capacity, if you have budget.  But this involves a certain amount of advance planning and risk, since you can't count on being able to upgrade "in the heat of the moment" as you watch the waiting room count approach your webinar limit.  And it's pricey, especially if you only a few more attendees.
       
4. Don't worry about it... if people are unable to attend, you can send them an Email with a link to the recording URL.  (See the "Follow-up email to absentees" section in this Zoom Support article.)