system
Given the following post, respond as if you're commenting on Reddit:
human
[Quantum Leap] Was it ever explained how the center responsible for tracking Sam Becket's historical changes were immune to those changes?

Sam's buddy Al and the computer systems were able to track timeline changes.  Al, like Sam, remembered the way things were AND how time changed.  How were they immune to the changes so that the new timeline didn't overnight their memories?
gpt
Sam is separate from the timelines he changes starting from the moment he leaps into the Quantum Accelerator. Not including his swiss cheese memory, Sam only remembers things from his starting timeline. Sam's mind rarely ever in the present for the changes to take hold, which is why it doesn't overwrite his memories. 

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AL, on the other hand, is linked to Sam via Brain waves through the Quantum Accelerator and that's why he's the only one who can see and hear Sam. Sam is sort of an anchor point for Al and the AI ziggy.  The only reason Al knows how things are changed is from the Ziggy telling him. 

For example, when Al is fighting with a Congressional committee to fund Project Quantum leap, Sam is trying to rescue a young woman studying to be a lawyer in the 1960s. The moment Sam saves her thus altering history, the head of the  Congressional committee instantly changes into the present-day version of that girl who is now the head of the congressional committee.