This is a high resolution photo of the Sphinxes. Yes they differ slightly, and this sort of attempt to differentiate them was 'normal' in sculpture of the period.
Also the Ministry of Culture released this diagram of the tomb, showing what has been excavated so far, with the sphinxes at the entrance. Michaelis Lefantzis is a brilliant architect, so the architecture is accurate, but the details of the Caryatids as restored are conjecture still; I know this is confusing people, so it is worth clarifying.
There were strong links between the Argeads and the Hecatomnids, both in terms of proposed marriages and adoptions and sharing artists. But I am aware that my research tends to make me think "Hecatomnid" in terms of links.
Let's Talk About Amphipolis ...
These bearded male sphinxes from the Persian Satrapy of Caria are very much in the Achaemenid style.
There have been some rather odd claims made about there not having
been any Greek Caryatids or no Greek sculptures of Sphinxes in the Late Classical and Hellenistic periods ... and in
fact two Macedonian tombs at Vergina have sphinxes.
The first is from the throne in the so-called Tomb of Eurydice, dated by a Panathenaic amphora found nearby to 344/3 BC: photo above.
Other examples of thrones with sphinxes have been excavated at Delos - see here: Andrianou, Hesperia 75, 2006, pp. 219ff
British Museum; ca. 400 BC.
BM), showing that the Nereid tomb was decorated with sphinxes just as the 'old' Lycian tomb represented in the frieze on the monument had been, as in the photo above.
There are dozens of earlier Lycian tombs decorated with Archaic and archaising Sphinxes, eg here. There are also sphinxes on the Lycian Payava Tomb, which is dated by inscription to 375-362 BC; here.
This is an Attic stele with a sphinx produced circa 400 BC for Archiades son of Hagnus and Polemonikos son of Athmonon (BM).
This is an early Classical rhyton from Athens of a sphinx wearing a saccos (BM).
There are lots of sphinxes linked to Amphipolis - on coins of the city, the Lion Tomb, this Roman relief later built into a Byzantine church there - so the assumption must be that there was an ancient, possibly local, myth that linked the Sphinx and Amphipolis.
here and the photo to left - which again suggests an ancient link between the mythical monster and the town.
And don't even get me started on the Greek style sphinxes from Ptolemaic Egypt ...