Misfire DTC codes cleared themselves?

Weird question. I had misfire codes P3000 P3005 P3006 and P1315. The codes randomly all disappeared and the distance-since-cleared number hasn't changed.

We were going to try a final hail marry of unplugging the o2 sensors, then replacing the ECM since everything, and everything else has been replaced.

Weirdly enough the codes have vanished (and it hasn't misfired since). The car misfired once after getting new injectors installed and programmed but all of its other symptoms are gone so we are hoping it was a weird relearn issue.

What would cause the codes to vanish like that? It says the codes were last cleared 210 miles ago, which would be at the mechanic. It misfired 100 miles ago so I'm not sure why the codes are long gone. Even if I cleared them on accident shouldn't that have reset the counter?

I was under the impression misfire codes didn't clear themselves.

(Velar First Edition)