As for issues in regards to league:
You can alter your CMs to your heart’s content UNTIL you ask for scrambles or OOLs. Once the defender has committed (and before dice are rolled) you are committed.
If you start rolling dice and forget a CM or want to change a CM you are SOL. The die is cast (pun intended) and you are committed.
Now you can finish your combats and do your NCM.
Your NCM is committed when you post your build order. Until then, you can still alter it.
Your build order is committed when you post your income.
Note: Illegal moves can only be changed up until the start of the next turn. Once you start throwing dice, the mistakes of your opponent are committed, you have in essence - agreed to accept the illegal move. This is only to prevent issues like saying “wait, how did you get your transport there, you moved 3 spaces without a naval base 7 rounds ago! We have to fix it…” etc. I feel this is an issue that does more damage than just allowing the mistake. We’re going to assume mistakes are MISTAKES not efforts to cheat. Of course, if a pattern of this behavior becomes evident, then you should report it to myself or DarthMaximus (g’luck, he’s on vacation! I’ve yet to hear of him returning, so…it’s me or nothing for now!)
If YOU, as the contestants in the game in question, decide to allow a correction, then YOU are stuck with it. I admit that I will almost always allow an opponent to fix something like forgetting to annex a friendly neutral or walk into an undefended territory if they forget. Failing to realize I had another airbase and can scramble 6 fighters and the odds are HORRIBLY against you now, I probably won’t (unless you agree to give me a mulligan. lol.) Of course, as the attacker you have the option to retreat after the first round, so you’ve got quite a bit of advantage anyway. Mistakes, after all, can be attributed to the “fog of war” no?