Re: "We believe that .... "
"Jonathan Edwards (Brit triple jumper) once said he forgot how he jumped to break records and never managed it ever again."
Remember test pilots aren't young.
Jonathan Edwards' best jumping isn't a great example, he was the best at-doing-his-thing of his generation. Athletes often have a golden period where everything is at its best. The gradual degeneration of the body (from about 18 years old) being overcome by training and increasing experience, after a point the degeneration wins (it always wins eventually). In track and field, the sweet spot is often only a few years. With Edwards, his sweet spot resulted in him jumping longer than anyone had, twice, in the same afternoon. He was still largely untouched for the best part of a decade and went over 18m quite often but didn't again ever jump as far as either of the jumps he did that afternoon. He is still the holder of the longest jump and the world record* a record that has lasted almost 2 decades. He says he forgot, in a sense the inevitable happened but it must have seemed to him like he had just lost the knack.
For fighter pilots, the flying training is intense, partly because there's exams to qualify from and they want to know how someone is in an intense environment (e.g. a war). But to my knowledge the most intense training is long before a pilot gets trained on their specific plane and flying role. So they never really know how good they are. I reckon a lot has to do with the more experienced pilots being quite a bit more efficient with their effort than the talented youngsters. So it must really seem like they aren't as good but they are probably just (unconsciously) wisely doing less.
If you will, Jimmy Anderson was a quicker bowler when young but much more effective when older.
* - the longest jump is farther than the record as it was wind assisted to a degree sufficient to not qualify for the record.