What makes this interesting is that the intercalary month is clearly given as Artemisios, whereas we would expect Xanthikos, this also puts Kassandros’ death in 296 rather than 297, as usually stated (298/7 was not intercalary, 297/6 was). [POxy_2082] A dispute broke out between the generals of the Athenians, Charias the commander of the hoplites and Lachares the commander of the mercenaries. Charias seized the acropolis ... after the expedition and prevented food reaching the people ... in the war ... but Lachares with the mercenaries ... 2 ... established ... and expelled Charias and the soldiers of Peiraeus. After overpowering the men who had seized the acropolis with Charias, he sent them away under a truce, but Charias and Peithias and Lysander the son of Calliphon and Ameinias took refuge in the temple [of Athene]. They held an assembly and sentenced them all to death ... on the motion of Apollodorus. The soldiers of Peiraeus also captured Peiraeus with the [men] from the city ...
3 ... besieged [them] in Peiraeus. Cassander the king of the Macedonians fell ill and died on the [21st] day of the intercalary month of Artemisius. He was succeeded by Philippus, the eldest of his sons, who was king for  months ... the historian Diyllus the son of Phanodemus [ended] ... year, Philippus [the king of] the Macedonians ... died ...
4 ... and the golden [statue] of Athene, and from [this loot] he provided pay for the mercenaries.
Looking at the Macedonian inscriptions on the Packard Humanities site there are no embolismic dates, in the literature there is only the story of Alexander making Daisios a second Artemisios in Plutarch. This causes a few problems, it might indicate that the Macedonians always intercalated Artemisios; despite the Plutarch story implying that this was an unusual intercalation, the reason given, that Daisios was a month during which the Macedonians would not fight is clearly bogus, Demosthenes says Philip campaigned throughout the year
Some books assert that the intercalary month was that of the king’s accession, but this cannot be the case for Kassandros who captured Olympias after Artemisios. Pydna was in dire straits as ‘spring came on’ which elsewhere means Artemisios, there were negotiations and then a capitulation, offers of free passage, then a trial and attempts at execution, as well as continued campaigning during which Olympias was co-erced into sending letters to her commanders. 316/5 was intercalary, but this principal would make Panemos the embolismic month as the month of Philip’s accession. The principal is unsound and not evidenced AFAIK.Third Philippic
 When, relying on this force, he attacks some people that is at variance with itself, and when through distrust no one goes forth to fight for his country, then he brings up his artillery and lays siege. I need hardly tell you that he makes no difference between summer and winter and has no season set apart for inaction.
Which leaves the question, have we just assumed that because the Seleukid calendar intercalated the same months as the Babylonian (for which there is a wealth of evidence), that the Macedonians did? It seems clear from the co-incidence of the two calendars’ months where we have dual dates that the same years were intercalatory, but the addition of an Artemisios rather than a Xanthikos would be so quickly corrected our evidence would not show it.