I noticed the same and theorised that closing an over long bullet in a chamber as a method of finding the lands (or max OAL depending on how you look at it) is unreliable because the bullet is pushed in by the lnads but also retained briefly by them when extracting the round.
therefore the measurement using this method will be longer.
"An infinite number of monkeys banging away at type writers for an infinite period of time will eventually reproduce Hamlet" Thanks to discussion forums we now know this to be untrue.