The more enlightened aerodromes put a little note on the Jepps ;words to the effect of -"PAPI indications not useable below 200 feet". Valid on a stabilised approach.
However, on the 744, ground effect at (Cat 1- manual flown) minimums tends to reduce the descent rate and drive you a little high on the slope. Doesn't take much to change from 2W/2Reds to 3W/1Red; not a particular problem, as this is what you expect to see at 50 ft RA as you cross the threshold (on the 74).
Trouble is, pushing the nose down at that height at high landing weights (higher RoD's) to get back on the slope (not!) could possibly generate a "sink rate" warning due to the narrow margins, and (in my outfit at least) a little e-mail from the FDAP monitoring department. On the other hand, watch the PAPI's when the Autoland is at work. Always interesting, because it can be surprising sometimes, depending on individual runway settings, or for whatever other reason. Good old autopilot doesn't care, just sticks to it's job, which is invariably done well and usually far better than Yours Truly.
When manual flying, I like to listen to what the Auto Callout has to say as the threshold passes beneath. "50 feet" suggests all is well.