Zoom add-on

I'm now using a Zoom PRO plan and I would like to recheck on these points:

• PRO plan can host up to 100 participants only
• If I want to host more, I have to purchase an add-on which is 300, 500 or 1000 participants type with different prices
• For the add-on, would it be automatically applied to all the existing scheduled meeting I created BEFORE buying the add-on? For example, I created a scheduled meeting "A" last week, for end of November. I purchase an add-on for 300 participants this week. Then for this meeting "A" will it be able to host 300 participants automatically after the purchase and all the access link and passcode set remains the same?

Thank you in advance!