We have had more direct contact on this already, but for continuity on this thread I’ll respond again.
As far as migration guides go, we do have some documentation lying around.
None of these are however documented to a level that we feel it’s fit for the Reference Guide (just yet).
Hence, this information cannot be found there at the moment.
I did take the liberty to answer two distinct StackOverflow question regarding an Axon 2 to 3 migration, which you can find here and here.
Additionally, the root directory of Axon Framework release 4.x contains an API-Changes file, which contains all the important bits to be able to migrate from Axon 3 to 4.
Concluding though, as pointed out, none of these are written down in a format that they’re workable for the Reference Guide at this stage.
Regardless, I hope this helps you out Paul, as well as other readers of this forum!