This is SO Bristish Airways. You are lucky you got the suitcase at all.
They tend to "lose" suitcases all the time - and deliver or not deliver later. Occurance: more than 30% (undelivered with the flight) with me, way above the industry average, and LHR is not an excuse.
One of the reasons I'm Star Gold.
I still check BA once per anum and I'm always sorry I did it.