I'm sure the vast majority of posters in this section won't know what an Immediate Scholarship Reservation for NROTC is.
To answer your question, not much. Just as you would get different grades from two different judges at an Olympic event (say gymnastics), and one judge's score would not cause another judge to change theirs, you will get two different grades from the NROTC recruiters, and the USNA recruiters.
However, the ISR would give me confidence that my resume is in high demand in NROTC, and if USNA has most of the same selection criteria (they don't completely match up as USNA hs much more geographical emphasis), then I'd feel I had a really good shot.
If you're asking whether you should update your USNA file with this information... what could it hurt?