If every saddle you buy is the same exact saddle that might work to a certain extent. But different profiles of saddle might have you sitting in a different place on them. As will minor differences in the bike geometry.

However most any method that others have suggested are a reasonable way to position a new saddle on a bike to get a position you can ride till you decide you want to find out if there is a better position.

You seem to have the idea there is one and only one position that can be correct and any other is uncomfortable. For me, I can tolerate a different range of setback. For shorter rides I can push the saddle forward and put up with more strain on my hands to get a better power position over the BB. Or for longer rides I can move the saddle back a tad to be more comfortable on longer rides without the hand strain. And give up a little of that power advantage.

Though I don't move my saddle that often. I have a sweet spot and it stays there for most of the time.