Is it easier/better to do a Change of Rater NCOER or a Extended Annual NCOER?

They should have not let you have any unrated time- it's been over 6 months- that's long enough for a change of rater ( or use to be)

I do not know all the ins and outs of why you PCSed without an NCOER. 1 failure on your part for not being involved in your career development. 2 poor leadership, that includes everyone in the chain, from platoon sergeant to the CSM. Your new chain of command is correct, they have no reasons to do an extended annual just because you didn't get a COR from your previous unit. How can they verify what you did? If I was your rater, I will put all that time as non-rated. As a SSG you should be able to interact with superiors and be involved in your career. Did you at least got a memorandum or letter of continuity?

Probably good feed from Staff Utley. I've sat a number of ENL/OFF boards in my time. Although Navy, this logic probably applies. First you want paper to cover all your days with no gaps. Gaps become question marks at boards. Second, you want the period covered by the reporting senior who'd have better knowledge and continuity. People come and go. In general, an extension by your reporting senior to cover the time to your departure is best. We used to have these rules that an annual would get amended so the words covered the additional time up to 90 days. After that, new paper. If your reporting senior leaves earlier than you, the paper date gets cut at that point. The new rater can go NOB up to 90 days and thereafter do new paper. We see a lot of NOB gap fillers at the boards. Having gaps is generally presumed to reflect on the SM not paying attention to their paper. I've never seen anything positive about a gap.