If I recall correctly, not many of the shelf saisons from 2010-2012 were ever dated. Barrel aged stuff generally had a bottle number or batch number. Also, if those old Annas and Arthurs have gold caps, they are likely early 2012 or before. I believe mid 2012 is when they switched to the silver caps for everything.
Also, I'd send HF an email at info@... and this is the kind of thing I bet they'll get back to you with the real answer. I asked a similar question a while back in trying to date a very old Anna.