Thanks Neil, you're right just checked & I mistakenly obtained the 2627 FID from a 2013.10 Sensis img thinking it was the Navteq and they were the same so the intention had been to differentiate them.

Carty & yourself may be well be right with dual CN's eventually clashing, I know it's not recommended but have never had a problem with the Topo/CN combo but that said it's not something I would leave long term anyway if nothing else purely for the sake of multiple layers slowing the unit down.

The primary interest is not navigation it is - for short periods - the ability to "stack" the maps to pool all the POI's together for far deeper and more effective searches which I find very useful at times. The POI's have always been quite different between Topo & CN, but now also between the differing CN's. To me the benefits of this far outweigh the risk of a minor blip at the time, maybe not everyones cup of tea but I'm sure there are others who would also find this a useful technique. It's one of those little things in life you don't really appreciate until you try it.