OK OK – so I wasn’t being that clear but for everyone else I just got a reply from Garmin about transferring topo and the like from one device to another:
Thank you for contacting Garmin Europe.
Once a Garmin mapping product has been associated with a Garmin device
that mapping license will only allow the mapping to be used with that
specific Garmin device. If you have any other Garmin units that you
wish to use the mapping with the these will require their own copy of
the mapping software for use on them.
The only exception to this is for mapping purchased on pre-programmed SD
cards. As these maps are specifically associated to the card and not to
a Garmin device the card can be moved between devices and will provide
mapping within the device for as long as it is inserted to that unit.
Note however that there is no option for this software to be used on a
computer for any form of planning.