Thank you rgray & wonderings
I think I have a handle on the problem - finally!
It appears I actually had three problems;
a) I did not want to “sync” the iPad to my library, as I did not want to delete the existing files on the iPad.
I needed to select ond add music albums. So Yes, I had selected to manually manage the library files.
b) The iTunes library that I was trying to copy from is a shared library on our old iBook. (both the system and iTunes on the iBooks are old versions)
iTunes would not allow me to copy from the shared/remote library to the iPad.
c) While I had read that I could move the music files manually [ i.e. drag them],
I did not understand where to drag then to.
I would select the file, and try to drag it onto the small icon of the iPad, with no effect.
I did notice a blue border appearing around a list of my iMac iTunes library, but that was not where I wanted to go.
and there was no other destination visible.
The solution that worked was to select the shared library,copy the music from the shared/remote library to my iMac library
Switch to the library on the iMac and drag to the files to the now visible blue bordered iPad library
Everything seems to copy over quite quickly, and plays as required.
I spent most of the morning searching through every manual & web-site I could find, but nowhere was there any mention
of the magic blue bordered boxes/libraries, or the limitation on copying from one remote/attached device to another.
If only the rest of the world would do as I say, I'm sure we would get along much better.