Aircraft coding

[Icare9]

Big Tyke: As per Grahams explanation it seems likely that as DK267 "H" was lost on 24th August, by 23rd September LK635 was NA H when lost attacking Hannover, so either it or another aircraft was NA-H in time for their next operation. For what it's worth, LK635 was the last NA-H code lost on operations (although obviously other aircraft could have been "H" temporarily, but not at the time of their loss).
Most Squadrons had 3 Flights of 6 or 8 aircraft each, so the alpha code worked out nicely, but individual aircraft could have different letters depending on circumstances such as loss or repair as outlined by Graham As new aircraft came in to replace losses so they would be painted with any "missing" code and take that aircrafts place in the dispersal bay. If you look at aerial photos of bomber bases you can see these dispersal areas off the taxiways, keeping safe distance between each aircraft in case of explosion while bombing up etc...
Hope that helps!!