The current UCI rule states the nose of the saddle (they largely assume a standard 27cm saddle) must be 5 centimeters behind the center of the bottom bracket. Unfortunately the rule is enforced erratically. It has nothing to do with the older rules that banned recumbents. It is simply a safety rule. Based on the observation that riders sitting far forward can't ride a straight line and tend to fall a lot. Sitting far far forward also greatly increase the chances of going over the handlebars under hard braking. Center of gravity is just all wrong when sitting forward.

Many modern bikes, including many popular ones, simply cannot be set up to conform to UCI rules. Once a rider is emotionally invested in one of these bikes they will claim the UCI rule is simply wrong, with no understanding of the issue at all.

I sure do remember the days that Salamandrine references. Where I was it mostly got done by force of example. We had old sixday riders who sat rock steady in the saddle. Old white haired guys who seemed to barely move at all who were still fast.They had unquestioned authority, did not need to say much. When squirrels showed up they learned fast or simply were not seen again. Now it is all squirrels.

The pro peleton is no longer much of an example for anyone. The old pros raced 200 days a year unless they raced 250. It was a job. The new kids learned from the old hands and they all knew each other well. Now the pros race 70 days a year, or less if on the injury list. They know their own team, not the entire peleton. Each time out they want to make a big impression on their sponsors. So they take chances. And never learn the job.

My 1950 Bates has completely modern geometry. When I had the Gloria Garibaldina (decades before anyone knew it was collectible) it was a 1930s bike with completely modern geometry.

If you try to achieve the identical position on every bike you ride you will spend too much time fussing with hardware and not enough time riding. Ultimately you can't make them all the same. Don't try. They are different. Enjoy them as they are.