This isn't like BC from some generations where the 360 chipset was included in each X1. The games have to be emulated through software. Emulating the 360 on the X1 is difficult and the emulator has to be tailored for each game. Therefore, each BC game has to be converted into a downloadable XB1 package along with it's custom emulator. This means that every BC game can be considered a "release" on the XB1 platform. Since the original agreements and paperwork never mentioned the X1 or future consoles, it requires new paperwork and signatures from the publishers and any related rights-holders, such as musicians and car manufacturers. I'm sure it's a bit of a nightmare for many titles. In some cases, the game could be released but never actually sold digitally, but if so, that lessens it's appeal as a BC title because all this work costs money and it's helpful if MS and the pubs can make that back through new sales.