If an NCO gets a letter of reprimand, that's filed locally, does it have to reflect on his NCOER?

A locally filed reprimand usually results from a violation that was not sooo egregious. The eater and senior rate in this case have more options. If they choose not to annotate the issue in the rating and the NCO later fails in the same it other areas, it can be posted in the OMPF. So the lesson is not whether the issue can be posted in the rating, it is get your stuff together and fly right. Your leadership has given you an opportunity to keep your career on track. Thank you for your service.

It doesn’t have to in a regulatory sense, though usually it represents a significant enough event or shortcoming that an unbiased evaluation of the rating period would make note of it.
Any time I was hesitant to talk about something on an NCOER, I kept in mind it was an honest and unbiased document representing the truth. It was what it was, if something good, bad, or ugly was important or representative during that rating period, consequences of the document were also honest and unbiased.

The reprimand itself doesn't have to be referenced. Like a 1059 it's located in your file. However, the issue it references should be addressed. For instance, if it was a DUI or gross negligence that led to the reprimand, the rater would be remiss not to address it in the Soldier's evaluation.
If the reprimand were appealed and removed at a later date, the soldier would be eligible to contest the NCOER and have it removed.

Does it have to be? No.
Is it fair to those that NCO is competing with? No, but the Army isn't about fair.
Not referencing it would permit NCO to rehabilitate, but some may argue that it doesn't pass the integrity test.
Sr Rater and Rater call
Since it is local, this is the end of it once the NCO PCS.
Saw NCO who had GO LOR for DUI in DS School as SSG. Later promoted to SFC. I recommended him for position as ANCOC SGL, and Regimental CSM raised the LOR and removal from DSS. My response: CSM, DA decided to promote him despite this. Who am I to question DA belief that he has been rehabilitated. He went on to become a SGM.

depends on your rater and senior rater - usually a letter of reprimand is for an action/decision/inaction that is not severe enough to warrant punitive administrative action, basically a formal "get your head out of your ass" letter that carries a bit more weight then a 4856. If the NCO in question gets his/her act straight, it will be "forgotten" when it's time for their NCOER, on the other hand, should the NCO in question continue to make questionable decisions, it can and probably will be reflected in their NCOER. I have seen instances of both occurring.