I added the two pension amounts together, and they total about £3780, so that is pretty much equals the calculation you made above.
There certainly seems a lot to take into account when trying to calculate pensions!
There is a lot to take into account and I cannot urge people enough to attend a FAR Briefing as part of their resettlement programme.
The Forces Pension Society (Forces Pension Society - Fighting for the Forces and their Families) deliver the first part of the briefing and cover service and state pensions, tax, national insurance, commutation, death. A financial adviser then takes over to talk about everything else with a pound sign in front of it.
These briefings are held all over the place and the full programme should be available from the Resettlement Office.