Dyno Vs.Drag Strip Testing

I think the problem most have with dynos, is it often points to problems in the car they put it in. Just as YR says.
This agonizing scenario has played out more often than not. It was a reality I've had to face myself.
In 93, I replaced a junk GER converter with an old 9J, turned a 13 sec car into a 11 sec car overnight and found my missing 100 hp.
On another front... every trans has different losses, or diffs for that matter. Road alignments are not drag friendly.
When a dyno shows 500hp, your drivetrain does not see it. It see's the hp available in the gear changes.
Example: On my car, that is 4700 (converter) to 6500 and 5300 to 6500 x 2. (Fun to get groceries with too)