As in many other fields, data is a very important matter. We have to find our spare parts, adjust the timegrapher to the correct lift angle, etc., so it’s very important to have the right data at hand.
So far, Generale Ressorts published a printed catalogue a very long time ago, and that’s still the only source of data when it comes to matching mainsprings with movements. There are some suppliers that have entered some of this data (Cousins, Ofrei, Boley) into their own systems, but a generally available list of mainsprings and where they fit wasn’t available anywhere.