Hah! And I thought it was only me and my advancing age!!

I have found that only certain parts of songs I have learnt and felt comfortable with are sticking with me. I have a few that I am going to have to go back and re-watch the lessons so I can play the whole song again.

I agree, I risk being bored if I hammer just the one song over and over. But I think if I re-visit the lessons after a break from the song quite a bit of it will come back quite quickly and more will be retained in my memory. That has certainly happened with one song in particular that I have "re-learned".

There is some learning theory out there that you retain about 50% of something on the first exposure, but after a second exposure you might retain up to 80% and so on.

Well, can't help you much other than to let you know you are not alone. Sadly, I think repetition is the key.

Alf