"Base" disappears completely even in elite athletes if you stop running. Ask any "former D1" athletes like myself.
But then once we start running again, we pick it up much quicker than our peers and can achieve levels higher than our peers. This is not because of some long-forgotten base from 10 years ago. It is simply a matter of better genes and natural ability.
Just like in middle school where we would be the fastest in the school on minimal training, the same applies when we run with the local club (unless there are some talented or very well trained runners in that group).
I stopped running for about 10 years after college, I started running again a few months ago for fun (after 10 years of drinking, smoking, and literally nor running at all), do around 20-40mpw depending on the week, and I'm already doing most of my runs at 6:30/mile pace. For the first month or so I was struggling to complete a 5 mile run at 8:00/mile pace, but now when I go for a 10 mile run I can kick the last mile or so in about 6 minutes. Mind you I used to do 10 mile "easy runs" at 5:45 pace so I've fallen quite a ways, but the talent is still there.