Some small and fun lore references I found from the books:

1) the obvious one - lilac and goosberries !
2) yen wasn't in KM when the witchers trained ciri, visimer asked if it was triss because shes the one who was there
3) the guy from the first tavern want to write about the war ... geralt warn him a soldier will kill him for boots ... I remember in the books they said that couple of times lol

Im waiting for a Field Marshal Duda reference.