Right, I THINK I've managed to answer my own question, by the simple expedient - as suggested by Peter - of RTFM (Read The F***ing Manual!).
Page 12 of the Dimax 1200Z manual says this:
...........
One of the prominent benefits of the DiMAX® Digital System is the ability to store locomotive
data permanently such as address, speed step configuration, special functions, and the picto-
gram. These data are made available to all DiMAX® Navigators or other handheld controllers
connected to the DiMAX® Central Station. This data is available after every power up and will
not be lost after shut down. The names of the locomotives are generally user related and
therefore stored in the handheld controller only.
The integrated database stores up to 128 locomotives permanently. All relevant locomotive
data is shown immediately after the respective address has been put in a DiMAX® Navigator.
The address, speed steps, special functions, and pictogram are displayed here. The locomot-
ive is ready to drive without any further actions. The only thing for you to do is: select and
load the locomotive.
.............
The bit in bold is highlighted by me - this seems to be the answer I was looking for, in that apparently I DON'T have to enter the details of every single loco in the second Navigator, the new Navi reads the stored database from the central station. What it still does NOT really tell me is whether that data is actually then re-stored in the newly-connected second Navi, or if it is only reading it as required from the Dimax - hence if I took the second Navi to someone else's layout along with one or more of my own locos, then my Navi would NOT haveaccess to the database for my own locos - I'd have to enter the relevant ones up as "guest" locos (temporarily stored only) on the host's system.
Does that make any sense at all, and can anyone confirm this?
Jon.