LO means Loved One. I was at OCS this past Thanksgiving, Christmas, and for several federal holidays. Leave was only authorized for Christmas (1 week), liberty was authorized for Thanksgiving (3 days, Thu-Sat) and Christmas (2 weeks), and all other federal holidays were treated like any Sunday (nothing scheduled, but no leave or liberty was authorized).
If there is leave and/or liberty authorized for July 4th, the CO will issue a written brief weeks/months in advance. Staff will know about it because it would address their leave, too. Good luck finding a Candio that's seen it or even knows to look for it. The Thanksgiving and Christmas brief was issued in September, but by Thanksgiving everyone had forgotten it existed, and then by Christmas everyone had forgotten it existed again. The general policy toward that liberty was:
H-Class, Indoctrination Candidates, and Junior Officer Candidates: On-base liberty only
Senior Officer Candidates: Off-base, on-island liberty
Candidate Officers: Off-base, off-island liberty