I do the EXACT same thing on my pistols only.I keep an excel file on all(pistols..)round count, misfires, or any notable problems or surprises.
If i buy the gun new, i know every round fired if i bought the gun new. When i buy a gun "Used" gun i will take the word of the owner and if they say something like 500-800rds fired i'll always go with the higher estimate since most people i assume don't count and try and make a gun sound newer than it really is.