Just noticed that there is no provision for the alliance of the Byzantines and Sasanids under Khusrau II Parviz in 591 CE that defeated Barham Chobin and restored Khusrau to his throne.
There was certainly an alliance, but IIRC Khusrau brought only a tiny (+/- 50 IIRC) number of followers with him into Byzantium. The army that restored him was almost exclusively Byzantine, was it not?
IIRC when he returned to Persian territory troops rallied to him. The army was mainly Byzantine but with some Persians.
Quick check in Theophylact has Khusrau arriving in Byzantine territory with 30 followers.
On his return by the time the allies are fighting Barham he says the army is 60,000 strong and was divided into three divisions 2 of which are commanded by Romans and the third by Persians and comprises the "mede phalanx".
I had forgotten that part. That sounds like a Byzantine army with a Sassanid ally to me, as well.
The Armenian history which is attributed to Sebos talks of a Greek (i.e. Roman) army which includes 3000 Greek cavalry, 15,000 Armenians and 8000 Persian cavalry. Fair chance he is biging up the Armenians ;)