"I have created extra code in 'init' that loops waiting for the partitions to become available.
Now, at bootup, when you see this message:
Loading drivers needed to access disk drives...
You will see dots appearing on the end each second, about 5 seconds for the first loop, then a couple more seconds for the second loop. The second loop displays red dots, so you can see how long the wait has had to go into over-time.
If you don't have any USB storage devices plugged in, you only get a 3 second delay total.
The end of the story is I was able to save a session to the USB drive and it was recognised and usable at next boot. Yippeee!"