I have noticed an interesting inventory pattern on many of my recent shorthaul flights, appearing quite consistently:

J9 C7 D4 R9

Examples from flights where I hold tickets:

20 JUL BA1338 2055 LHR NCL 2205
03 AUG BA475 1450 BCN LHR 1610
24 AUG BA975 1705 HAM LHR 1745
21 OCT BA486 1640 LHR BCN 1950

The flights are clearly not constrained as BA is accepting local passengers and connecting passengers at the R fare (subject to inventory availability and fare combinability on any onward sectors). So far so good. But why would BA constrain D availability so heavily when R is wide open on such a consistent basis (which suggests a deliberate decision)?

My guess is something to do with corporate traffic (corporate discounts booking into D produce lower yields than non-corporates booking into R) and/or dual inventory (ET to CE upgrades subject to availability of D class, which could also but will not necessarily be a feature of some corporate contracts).

What do you think?