Hi LoriS2 welcome to the GoTo Community, thanks for sharing your experience.
This does appear to be expected behavior when scheduling a Webinar series. Anything that is changed in the current series, will affect all in the series.
If you would like to use follow-up emails going forward, you should create a new webinar series. Alternatively, you could run an attendee report after each webinar and compare it to the registration ID for those who did not attend and send them an email directly.
I understand that this may not be the outcome you hoped. I do see you posted in the Idea forum, we will share this with the team and leave the idea open for comments and kudos. Thanks.
