I'm not sure if I'm here to comment on time or whether someone has commented so already BUT as we spoke, Harry, I believe the best solution would be having a unified stadium pack with Classic Patch 14. CP14 already has 462 stadiums as of the latest release and naturally most of them (bar a couple historical ones) are the same as here in FIP 19-20.
Currently if I intend to play both patches I will have two separate stadium packs 20+ gb each, most of them being duplicates of the same stadium but with different IDs. And if, let's say,
@gonzaga were to release a new stadium and I wanted to add it to both patches, that would be double work every time.
I suggest you use the CP14's stadium pack as a base, just ignore the stadiums you don't need like Highbury, but keep the IDs identical and add new stadiums in coordination with CP14 to avoid future ID conflicts. Maybe
@GIGGIRIVA and
@acicog30 from CP14 can comment. I think this would benefit everyone and save HDD space.
Also, for those who use Jenkey's File loader it's even more convenient: create a folder like "Fifa14ModStadiums" or whataver and have a sharen unified stadium pack for every patch in the future which uses the same stadium IDs.
I would even suggest that we create a community "Faces" folder to be shared by all patches with EA faces converted from FIFA 15-20 and unique EA IDs (again to avoid having the same Messi face duplicated in CP14, FIP 19-20, etc - all adding up to dozens of gigabytes of duplicates).
Maybe also custom faces but that would be debatable since some people prefer default faces over poor customs, others like as many faces as possible, so this one might be not that straightforward.