I found a brochure scan introducing the watch that Arno sent me, but it doesn't make the claim of first with date wheel. Might be my memory but I could have sworn it did, or maybe there is another out there...

I'll carry on looking for the other ad, if it indeed exists. Even if there were other chrono movements with date wheels out there at the time, Valjoux didn't have one, so Heuer would have to have looked for a different partner. If it was nowadays, there would be all sorts of kickbacks and exclusivity deals going on between the watch and movement manufacturers, I wonder how those relationships were back then.