Just to clarify this, for record the only correct filter number is HG7Z-6731-A.
Let me reiterate: the only correct filter number is HG7Z-6731-A.
The Motorcraft online reference chart is incorrect and being updated. The FL500S is not the correct filter. Believe it, do not believe it; I do not care. Use it and you will save a lot of money on filters, which is convenient for when you'll need replacement engines.
I suspect that the reason for this has to do with the insured quality of the anti-drain back valve. Almost all modern oil filters will have an anti-drain back valve which will prevent oil from draining out of the oil filter. Hence, these valves will help the engine to have oil pressure as soon as the engine is started. With modern high quality oils maybe this valve's function isn't critically important as in the worst case, maybe it takes a second for the engine to have oil pressure. No bigee.
However, in the case of the NFGT, there is quite a bit of external oil plumbing typically not found on today's production cars. Principally this is because that in addition to the "embedded" coolant to oil cooler, the NFGT also employs an external (large, vertically mounted) air to oil cooler. Impressively, this oil cooler even has a fan to further assist cooling. Anyway, with all of the hard line external plumbing, it is possible under probably unlikely scenarios, for the oil system to lose its prime. This wouldn't be good. The shop manual has a specific air-bleed-purge scenario in case any of these external lines/components needs to be serviced.
What I strongly suspect is the case, is that Ford incorporated a really higher-than-ordinary quality anti-drain back valve in this specific oil filter. While a lesser quality (cost) oil filter would likely work, there's probably a couple of odd-ass-car-angle parking scenarios that exist in the wild that - coupled with a failed or slowly leaking anti-drain back valve *might* cause the oil system to lose its prime. These are probably very unlikely scenarios.... but how lucky do you feel?
After this investigation, I'll shamelessly retract any recommendations to use something other than this filter. It wouldn't surprise me at all if a John Doe could get 50,000 trouble-free miles on an FL500S (it's not going to burst or anything like that)... but that once a decade downward, left-leaning mother-in-law driveway combined with a minute leak in the FL500S valve may cause that motor to go boom. And who would want to have their GT go "boom" at the mother-in-law's house?