Always found when buying bikes a full service history only ever tells half the story, from my experience normally means serviced as per and a bucket of water over it on a Sunday.
My preference has always been a combo of some where in between,receipts for oil/filters go a long way and gut instinct covers the rest.
The last bike I sold was twenty years ago, that most certainly didn’t have a full service history...the problem I had two buyers turned up at the same time and when they realised that the bike didn’t have a full history but the owner was OCD it nearly turned into a fight because it suddenly dawned on them it was a chance in a lifetime,the guy who didn’t ride during the winter got it, and as and when I ever sell any of the others I have the same applies.
Spent yesterday cleaning the K with a pointed sash brush and silicone yesterday clean??? Like the day it came out of the crate but it doesn’t have a stamped up book