Collbar Maybe the defence system is not required untill a later point in the contract. If the wiring is in place its only a few hours to fit the external bits surely!!
Whilst I applaud your thinking, and I don't know, but if it is anything like the VC10 farce, one would wonder..
Apparently when the VC10 fleet was rewired at EGNX, (from there it went down to Bournemouth to have the tanker pods installed), common sense (and it was offered to be done free of charge rumour has it) would have been to put all the tanker wiring through all the disturbed pressure bulkhead seals during the rewiring phase, then it was a simple job of routing and connecting up, however that was a different contract, so when the tankers arrived for the refueling fit all the pressure bulkhead seals had to be split open again to allow the tanker wiring to be addded to the looms....