I have not done this specific thing, but given what you have and what your target is, there are a couple of things I can tell you to watch for. From SP18 to SP23, there are 3 major issues introduced in the intervening Service Packs:
a) The format of the User Overrides has changed (introduced in SP20), your users will probably find themselves having to delete their existing ones, and completely recreate them.
b) The encryption algorithm for passwords has changed (introduced in SP22), there are specific steps to handle this (as you will see in any Xe Service Pack One-off installation manual), but the steps for testing and fixing this can be daunting if your CNC skills are not strong. You will have to install one ESU, currently JD25239, with more information here (
Solution 200815107).
c) Issues with posting were discovered in both SP19 and SP21. The details are here (
Solution 200782516) and here (
Solution 200782558), but at this point, it should boil down to 2 or 3 ESUs that you'll have to take.
This document (
Solution 200950044) might also help. It talks about jumping from SP17 to SP23 on the AS/400, but many of the issues are the same.
Given all these issues, you might want to reconsider the phased approach.
