In practice this would take longer than the 27 million years stated assuming 2 things: that the computer doing the guessing doesn't try passphrases it has tried

In practice this would take longer than the 27 million years stated assuming 2 things: that the computer doing the guessing doesn't try passphrases it has tried in the past and that the user changes their password at least 1 time (more likely multiple times) within the 27 million years. This is contingent upon somehow not changing your passphrase to a passphrase much much higher up on the list of what the computer will try to guess. What are the chances of this occurring and what are the chances of the opposite occurring where the user's correct passphrase is somehow next on the list yet at that time the user randomly changes it to the passphrase at the very end of the list? Would this then mean it is better to keep the same passphrase forever or to change it?