Reminds me of a shop in Melbourne that many older Australian motorcyclists would remember - Modak Motorcycles.
In this case the human encyclopedia wasn't an old geezer, but an old woman. The late Jean Beanham must have been in her mid 80's the last time I saw her behind the counter, but she could rattle off from memory the part number of pretty much any part of any old British bike that ever existed. You could walk into the shop with some obscure part, she'd glance at it and tell you exactly what it was, what bikes it fitted and whether she had one in stock.
She worked full-time behind the counter until her death in 2016 at the age of 91 (although I saw another article that said she was still working at 92, so perhaps she was coy about her age).
Motorcycle riders will gather in Melbourne in October to honour Mrs Jean Beanham who worked at Modak Motorcycles right up until her death in June aged 91.
www.webbikeworld.com
I'm pretty sure the shop has closed now but Modak still appears to be in business selling old British bike parts on eBay.