So what else might be different about them? Gear ratios in particular. Might be the position of you on one bike allows you better power transfer.
From one time to the next I may or may not be able to match a previous personal best on any segment. And many times, I can best or match a segment time after having 4 to 10 days off the bike as opposed to what I can do when riding regularly.
Also realize the bike you might do well on for a short ride might not be the bike you do well on for a long ride.