Not commenting on specifics of the case BUT can be difficult for Seniors who know something is happening but unsure because it is low key whether their presence is desired...................not required, desired.
If everybody assumes X is invited apart from X then its hard to apportion blame to X.
Leaving do's can be a difficult one whether service or non service but if want to ensure someone is there then important to make sure they aware of invite, remind them a week before and remind them on day.
If All do not attend when invited, reminded a couple of times etc then could be personal but generally in a group of a reasonable size there will always be one or two who would or at least ensure proper apologies known in advance.
Getting people collectively to ignore is kind of hard to do (and enforce) as people don't like being told what to do in their own time and also more likely to tell people of it as well.