Hi, my Mum is in 6/7 th year of mixed A & VasDem and struggles with many conversations but loves talking about the past and becomes lucid, animated etc. I know for a fact she mixes some genuine memories up but it really doesn't matter. Every Sunday dinner time when Mum and Dad are with us we make a point of talking about someone or something to do with the past and have the iPad handy to bring up a song, film clip, headline, etc and Mum loves it. Last week I remembered her love of Glen Campbell when I was a child so we had a great sing-a-long! She could talk about making the family dinners, old recipes, the house etc and listening to Glen on the 'forces radio' programme.
We had previously made up a CD of the music, films and stories we associated with our parents and growing up (downloaded songs from iTunes) and made a scrap book with all lyrics and a memory 'box' on each page of who remembered it and why ...5 years on it still brings tears of joy and stories and memories. It was also amazing to hear which songs the grandchildren remembered, one of them remembered Nana and Gramps dancing arm in arm in the lounge to Moon River by Andy Williams when she was about 6 so that was her favourite memory!
I think I get a lot from hearing Mum chat about the old days, helps to remind me who is still there behind the dementia mask. Like you were, some of her memories ( and 'unexpected disclosures'! ) are surprising but I guess we all have little secrets! Enjoy would be my advice