[PIF]

9 were built, 1 was damaged (repaired?), 2 shot down. Leaves 6 A-50 and A-50Us

[FtrPilot]

I believe they are saying that 5 of the 6 remaining A-50s are not flyable (Operational Ready (OR)) or are not Mission Ready (MR).

Not MR could be caused by radar equipment not functional. The aircraft can fly but cannot perform its mission.