In order to make things consistent with the reels, they must all be the same make and model, and be spooled with exactly the same amount of line. Mechanical line counters actually count the spool revolutions, and not the actual line. What we often do is “calibrate” our reels every once in a while.
Like you did, we measure out the line and read the counters, marking each reel as being “OK”, or “+5”, “-10”, etc. depending on how far off each is. That way we can always know we are letting out the same amount of line on each reel.