Yes, you are right, I was fortunate that CCM left soon after I arrived and the larger part of my tour was with Boots. I then had a near death experience with Mike d'Arcy - not his fault but he was the operating pilot, but that is another story.
On the CCM-Boots bit, I was summonsed to the staish's office to change the safe combination on their handover. CCM gave me a piece of paper with his combination. I opened the safe and cleared the combination. Boots then gave me a piece of paper and I reset the combination.
I still remember the numbers of each - 44 - 50 - 01. I never told either that they were using exactly the same numbers
The only thing in the safe, IIRC, were the duplicate keys to the SSA bunkers.