@Lascaris thank you for the info on both lorries and trains! Especially for quoting Papagos, after all you cannot give more precise information than the OTL General Staff.
Lascaris, I am also under the impression that the remnants of the XII and XX Divisions were retreating
with the Commonwealth. I remember reading of some of their men being in Crete. Also the Dodecanese Battalion that formed in Egypt seem to have had men from the Greek Campaign Dodecanese Regiment. The Dodecanesians there are listed separately from the local
Egyptiotes. Perhaps the XII and XX remnants in TTL are larger than in OTL. What is your take?
If that is the case, then these men are excluded from those evacuating from the Kalabaka railhead as they are retreating using their own and mostly Commonwealth motor transport.
Could some elements have road marched out?
I doubt they could march via the Thessalian Plain. They had already marched a long way already. It will have to be leapfrogging via trains or the lorries Lascaris' mentioned.
But elements of the Epirus Field Army Section (EFAS) could theoretically march to another direction since they gained precious time: to ports. During the war, part of the 1st Army Corps (II, III, VIII) supply came from these small ports, so coastal shipping existed. The men of the VIII Division were locals from Epirus so when the everything is collapsing they will just go home- there is no real incentive to escape to southern Greece. However, the men of the II and III divisions were from southern Greece so they had incentive to brave sailing without escorts in small ships or march overland to cross to Peloponnese. A few of them may end up in Crete. After all, the men of the V division had reached Peloponnese by the 1st week of May, even though they started from a more northern point and had to stop for a couple days to surrender their weapons.
It will depend on how long Thermopylae Line lasts. If for example it can hold for 4 days and the accumulated additional days mean that Germans invade Peloponnese at May 1st or 2nd, then some veterans can be saved this way. Certainly not the equivalent of a division, but of a few battalions.