Many thanks for your reply - I didn't know you could create these OS-aware links, this is going to be handy!
I edited my original question (just before I saw your answer) to mention that the missing P: drive was no longer listed to the system, so unfortunately these links couldn't be created without a little bit of additional work. With this, and while in Disk Manager, I see that I could create a virtual disk which I then did onto a file on one of the data SSD's, and was able to name it the P: drive. I then created the MUSIC directory here to complete the missing path (I hoped). [I find that as I get older I find it hard to remember some things I used to know in the past].
On running the Bandlab Cakewalk updater the process thankfully completed. Cakewalk still runs well. I could see that it was writing to the P drive and later to the C drive. I knew the original Bandlab (version) was always installed into the C drive so that's good. I then had a look at the P:\MUSIC folder and could see a 'Cakewalk Content' folder and inside the following 3 folders: Cakewalk Core, Cakewalk Themes, MIDI Library.
The original P drive was an old, slow and noisy HDD. The PC system I use is some years old with various HDD/SSD changes. It's likely that the original P drive was used at some point with Sonar, hence some legacy paths that I should have tidied up at past install/update stages.
I'd like to return this virtual disk space back to the SSD holding it (meaning the P drive would also disappear) so, is there a relatively simple way to have this Cakewalk Data structure & contents (192 MB) moved to one of the data SSD's and so that Bandlab Cakewalk is aware?