Coming back to FSX after a break, I've become confused (well, more confused than usual

) about the various AFCAD files that have accumulated. I have all the latest xtreme versions, plus the 2 VFR Sceneries, and their AFCADS. I also have a folder UK2000_High_Position with AFCADs originating (I think) from the old FS2004 VFR sceneries,which I've inactivated (the sceneries, not the AFCADs) as they don't work well with FSX. But in that folder are two AFCADs for each airfield - one with the format EGxx_afx_UK2hi.bgl and the other with the format FSX_afh_EGxx.bgl. At a quick glance, these seem identical, viewed on the ADE utility. There are some 'MAX' versions in both formats.
Can someone remind me why there are/were 2 formats? The UK2000_High_Position folder is situated below the newer sceneries and so it doesn't (or shouldn't, anyway) interfere with them, but I keep them there and active as they sometimes are a good fit with the FSX default airfields, north of VFR Vol2. If not a good fit, I either delete them or tweak them.
Looking forward to the remaining VFR Volumes, though!