Updating you as requested --
The "long-established" Tuesday sessions at the Tappit Hen in Stirling "ceased years ago", I was told.
The only folk nights at the Lade Inn at Kilmahog nowadays are Saturdays when it's a local guest "act", no indication of any other performers being allowed.
"Traditional music sessions" at The Old Rectory Inn, Callander take place on Sundays from 5 till 8 pm and on Wednesdays from 8.30/9 pm till 11/11.30 pm. (Not quite as billed - this is actually two guys with guitars miked up and playing mostly the "popular" side of folk and American/60s/70s covers with occasional Scottish songs thrown in. Very friendly, and they will invite other singers or players up for a brief "turn" when they take a break themselves. It's a very small bar!)
Stirling folk club happens on Mondays, but the week I was in the area they had a booked guest, it was a local act, but the admission price advertised on the website seemed a bit on the expensive side considering ...
I was unable to get a reply to my enquiries about folk sessions at The Settle Inn, Stirling, either by phone or email.
Dunblane folk club apparently still meets on Sundays in the Dunblane Hotel, but the hotel staff denied this when I phoned, only mentioning a "jam session" on Tuesdays instead, but I didn't find this out in time to sample it.
Aberfoyle itself - the Forth Inn has a "folk music session" called AbTrad on the first Friday of each month, but again this was the "wrong" week for my visit so I was unable to sample it.

Of all the emails I sent enquiring about sessions or clubs I'd seen advertised, only one responded to me before I left home. Another replied a day late. But the rest didn't reply at all. Hmm...

I may have been misinformed about some of the above which I was unable to sample by personal experience, so would welcome any further updates or corrections as and when other Mudcatters visit the area.