They could be. There is reference that the 7x54mm was a shorter version of the 7x57mm based on that case head size, but there could also be some as sort of a wildcat of the parent 6.5x54mm case for shot out bores. Same goes for the 7.63x54mm Greek, it could simply be the Greeks changing the name of the captured Turkish 7.65x53mm rifles, or again an experimental calibre to open up worn out bores with the same case to increase service life on the cheap. Sort of like the Italian 7.35mm Carcano.