GPS datum shift?
Yes, about 2 nm, and no datum "shift".
The British Admiralty Leisure Folio SC 5640 The Virgin Islands (1st ed 2003),
sub-folio 5640-2, has a wreck marked "PA" (position approximate) at coordinates N 18 deg 35.85' W 64 deg 32.00' (WGS84 datum).
The correct Chikuzen position, N 18 deg 37.130' W 64 deg 30.969' (WGS84 datum), falls outside sub-folio 5640-2, however it can be located on the adjoining sub-folio 5640-3, which has no "PA" wrecks marked in the East semicircle of radius 4 nm centered at N 18 deg 37.130' W 64 deg 30.969'.
Since 1' lat = 1 nm, you can check that the difference between the PA position and the correct one is ballpark 2 nm.
Anyway, I was in the area around Nov 22, 2012 bareboat chartering and the sea state was good for a dive. Unfortunately, I could not locate any buoys. Nor could a large catamaran with at least 12 divers aboard. We both criss-crossed the area together for about 20-30 min to no avail and left.
Does anyone know if the buoys were removed on purpose or broke off?