**Edit: ** I got a different value for 580EX II and older Canon models. Perhaps it has to do with 580EX version II.

D30 reads 580EX II as 0
D60 reads 580EX II as 142
300D with custom firmware reads 580EX II as 222
30D reads 580EX II as 142
All of them read 380EX correctly as 133.

6D, 7D, M5, 1000D and R6 read 580EX II as 145.

Original post:

The tag [MakerNotes] 0x001c Flash Activity seems to be Speedlite models. The number changes with a different Speedlite attached. What I have tried so far:

132 540EZ
133 380EX
134 550EX
136 ST-E2
141 430EX
145 580EXII

For 1000D, the tag [MakerNotes] 0x0013 Canon Camera Info 1000D 0x0013 also changes with the same number depending on the Speedlite model.

For 6D, the tag [MakerNotes] Canon Camera Info 6D 0x0015 also changes with the same number depending on the Speedlite model

For 7D, the tag [MakerNotes] 0x0013 Canon Camera Info 7D 0x0013 also changes with the same number depending on the Speedlite.

For R6, the tag [MakerNotes] 0x09a5 Canon Camera Info R6 0x09a5 also changes with the same number depending on the Speedlite model.

I am waiting for another Speedlite owner who has some different Speedlite models.