Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
Scoutbook and IA are supposed to display the same data as they use the same database. Long term, the Scoutbook user interface will be retired and all calendar activity will be performed with the IA user interface.
That said, there are known issues that are being worked on by the developers. Watch the Scoutbook Change Log for notices of updates.
NOTE: Currently the IA adds everyone who was invited to the event as a participant of an activity (e.g., campout) if you link an activity. Remove those who did not attend and you do not wish to be included. (The plan is to have an option to include only those marked attended, but that is not in the system yet.)