Back in the dark ages when we used a distributor tester to check the centrifugal and vacuum advance operation, each distributor had its own advance curve- - - -a certain number of degrees of advance for a particular RPM. Even things as simple as different rear end gearing, tire size, or transmission type could require a different advance curve. That's why there are different model numbers stamped on the breaker plate.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!