While the bulkhead may have been secured in the IX HQ at Akrotiri it was still recovered.
While I was not on IX IIRC this is what happened:
A 617 crew managed to free the bulkhead whose loss was discovered before the 617 Vulcan had departed. Under a pretext it was searched and then a guard mounted but the bulkhead had already gone. Not to UK but to Masirah in a Belfast!