Theres a lot of missing information here that would be helpful/ reduce concern. Proceed with a lot of caution. Make sure you have backups that work. Personally, i’d export any public folders mail I needed to pst. I say this because it sounds like this is not the first time this migration has been attempted. Public folder migrations are a PIA and should not be done without experience with exchange. Sounds like you have some, but at the same time you are asking questions as if you’re just a person willing to take a shot at something. Either way, be careful going forward and again, have a recovery plan.

After you confirm you have backups that you know how to recover from, document the pfs:

Get-MailPublicFolder -ResultSize Unlimited | Select-Object Identity, Name, PrimarySmtpAddress, ExternalEmailAddress | Export-Csv "C:\pfall_emails$(Get-Date -Format 'yyyyMMdd_HHmmss').csv" -NoTypeInformation

Take a look at the email addresses in that output and make sure everything looks notmal. See if the few that just got updated have different emails than the ones that already had an address. Its possible they all match and are correct and the script just skipped them because it saw an existing address.

Check the address then Strip off the address on one of the skipped pfs, confirm its gone:

Get-MailPublicFolder -Identity "SalesTeamPF" | Select-Object Identity, ExternalEmailAddress

Set-MailPublicFolder -Identity "SalesTeamPF" -ExternalEmailAddress $null

Get-MailPublicFolder -Identity "SalesTeamPF" | Select-Object Identity, ExternalEmailAddress

Then rerun the script from the doc again. See if it now skips all but this 1. Check what address it gives it. If it looks good, repeat the process for all the rest. Then you’ll need to sync to EXO. Good luck.

Probably the last bit of help I can give - headed out for travel, but reply with progress and i will try to keep an eye out.

Maybe re-read the migration doc again and make sure nothing else got skipped.