It's probably a Dual Inventory fare, but not displayed properly - they look like NHE4AP/DIF4. At least what Matrix shows is not the DIF fare, though if it says it is in WT+ it has found the DIF fare. Did you cut off the part of the fare after the / ?
There are two fares like this:
QLX4S4T1BAQ for 230.00(USD) and QLX4S4T1/DIF4BAT for 417.00(USD) (including carrier surchage, excluding passenger taxes and airport charges).
The first books into Q and sits in World Traveller and only requires inventory in Q.
The second books into class T and sits in World Traveller Plys, but needs inventory in Q and T.
The "valid for specified account" means that it can only be sold by some accounts, in this case the internal BA online account. So you can't buy this from another travel agent.
Last edited by flatlander; Dec 20, 2016 at 4:12 am
Reason: Updates