Is there any requirement that NCOER bullets for M-Day soldiers reflect only work performed within the National Guard during drill?

There is no requirement for that. I incorporate civilian education, physical endurance events, civilian shooting events, leadership and mentoring from civilian jobs, etc.

The bullets need to show a direct relationship to military duty.
How did continuing education enhance his MOS skills, How does his civilian job enhance his skills.

I can think of some off duty stuff that can be valid :
o obtained personal trainer to improve fitness; increased APFT score by 60 points.

o Spent over 100 personal hours planning and preparing AWT training; 85% of unit considered trained during rating period.

Stuff like that are perfectly valid. I know because I have similar in my own NCOERs

A few specific examples....

(1) Servicemember is applying to be a JAG officer and works as an attorney on the civilian side. Would his private practice be considered relevant to an M-Day NCOER?

(2) Servicemember successfully lobbied the House / Senate to secure language in the NDAA for changes to military personnel policy. This was done on his own initiative on his personal time and he received no pay or compensation from anyone. Is that considered relevant to an M-Day NCOER?

(3) Servicemember volunteered for local community organizations -- specifically serving on the Board of Directors for a veterans service organization and an urban sports league. Is that considered relevant to an M-Day NCOER?

(4) Servicemember serves as a Contracting NCO and maintained professional credentials (law licenses and PMP certifications). Do those enhance his skill in his MOS? Is that considered relevant to an M-Day NCOER?