I bought a used Sony Xperia XA2 phone and it has stock Android 9 installed. The /e/ OS install directions say to install from Oreo (Android 8) but I see that there is a test build of /e/ for pie. However the test build of pie chart on the following page says to upgrade from Oreo:
How do I get my stock device to safely have Oreo on it or can I just start the upgrade from stock Android 9?
Marty
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You’ll be OK from Stock Android 9, no problem. I last did this on 3Feb21 using twrp-3.4.0-1-pioneer.img
Advise carrying out the copy-partitions step just to be on the safe side.
Nice-that’s exactly what I was wondering about. I have never re-partitioned my phone intentionally except to fix a phone years ago. I found out then that these ROM zip files sometimes re-partition your phone when Android upgrades so there is no going back because the nandroid backups don’t restore right. I guess that copy-partitions file takes care of that?? I’ll make sure I do it. I wasn’t sure if this was just for Oreo. They need to put specific install directions in there for pie even if it means just linking the Oreo directions.
Thanks! 
Marty
The install instructions have been slowly improving over the last year and now, for the XA2 specifically, they are almost there in my opinion. I’ve suggest changes in the past which the e team have actioned, only for the changes to disappear a few days later!
The steps are the same no matter the OS version and the pie testbuild is obv. a testbuild so no instructions required. The instructions link to the currently supported OS release, which is oreo at the moment but will be Q next week (fingers crossed).
The copy-partitions zip, I think, simply copies the contents from one slot to the other to do what it says in the instructions. I’ve tried to understand exactly what it does but I don’t understand the code! But my guess would be that the actual partition structure is not altered and some partitions are ignored completely. I also read somewhere that it copies info from the active slot to the inactive slot, rather than from a to b specifically, which would make sense. Otherwise you would always need to know what slot you were installing, which can be confusing for the unitiated.
I don’t know about nandroid backups, but if you are expecting it to work you’d better research the forum. I’ve got a feeling they may not.