I typically do 1 to 1, but in the case where more than one related STC is applied at the same time I might put them on the same form. For instance, we installed pulselites, wingtips, and recognition lights, and we opted for HID lights, the wingtips/lights were one STC but the HID option was a separate STC and the pulselite system was a third STC. I put all three of those on one form.