Yesterday I browsed posts in the Mounting Partitions sub-forum of Hardware support, and found some very instructive exchanges, particularly about UUIDs.
Among others was the use of MintDisk - my attention has not been attracted to this before. I found that selecting the option to Mount ntfs Partitions produced a dramatic effect - all my access problems in Celena are solved!
In spite of the fact that some of them are only mentioned in /etc/fstab by a commented-out line, they all now appear, with permissions for me to read and write! Wonderful!
The only remaining problem in Celena is the rather frequent failure to proceed through the boot process beyond the opening of the Gnome screen - no movement along the progress bar. Re-starting with [Ctrl-Alt-Del] is sometimes required several times, or even a Restart. The last resort is Recovery Mode. Any suggestions?
Many thanks to many people who have given advice - especially for introducing me to Supergrub and the Grub tutorial.