PMDG FMC ( and any other 3rd party airplane FMC ) don't read the scenery database, they have their own internal database, which should be kept updated and (hopefully) would match the scenery used.
In addition to that, the FSX/P3D scenery format doesn't even ALLOW for a scenery to have SID/STARS. These have been added to the .BGL format only with MSFS 2020, that's why every airplane that has an FMC in FSX or P3D has its own separate database: the information is just not there in the scenery itself.
Which means, as a general rule, regardless which scenery you use, whenever you have an issue related to SID/STARS in FSX or P3D, it's never a problem of the scenery itself, and it's always related to which database the airplane has loaded.