Possible Error in OBAT07 in MobHack
 

In the UK OBAT, unit 519 is showing as unknown for the nation.

Re: Possible Error in OBAT07 in MobHack
 

Marked as not nation 7 (UK) but not removed from the OOB.

Not an "error" - just a simple clerical removal process for iffy stuff - saves deleting it and then looking through hundreds of scenarios to see if it was used by somebody.

You will find plenty of items marked as "unknown" if you troll through the OOBs.

Re: Possible Error in OBAT07 in MobHack
 

Open the MBT USA OOB in MOBHack.
Click on File then click on Database Check Utilities
Click on Formation Checks tab then the Broken Links and press " Run Search"

In this case every one of those are nation zero and that is a perfectly legitimate way to build a formaton and hide those sub formations from players to buy singly as they only exist as part of the larger formation

The unit you found, the P2V-5 Neptune was removed from purchase as unnecessary to the game and forgotten about when the game was still in DOS ( I *think* becasue it was never used as a bomber by the RAF but that was a L O N G time ago )but there will be dozens more in all the OOB's in both games exactly for the reason Andy gave. Sometimes I re-nationalize a unit that needs to be taken out if I'm not sure if it might be used in a scenario or campaign that used to be a big job and they are of no concern until the OOB starts to get full which is not an issue for that OOB. Sometimes if I'm bored and have spare time I remove them and check for scenario / campaign usage but that job is a PITA so many are just left and they do no harm

If you keep looking you will find more. none are " errors". Use the same MOBHack database utility and click on "Unit checks" then " Find Foreign units. In the Brit OOB there are 4. Two are units and 2 are notation markers

Foreign uints found:
Unit 477 - Jaguar (class 44 Fighter-Bomber) is assigned to nation 0 Unknown
Unit 519 - P2V-5 Neptune (class 62 Level Bomber) is assigned to nation 0 Unknown
Unit 800 - NEW ARTY UNITS (class 216 NO UNIT) is assigned to nation 0 Unknown
Unit 900 - NEW MISC UNITS (class 216 NO UNIT) is assigned to nation 0 Unknown