I wonder if the increased compatibility is more to do with changes to the mapping than to the firmware? 13xx/14xx has not been updated since 27 Nov 2012, version 6.20, yet anecdotally in the last year or so there appears to have been progressively less reported problems using unicode mapping in older units, and especially in reports about 1xxx.
Even Garmin seems to be a little confused about unicode EU and 1xxx. I had an interesting series of conflicting events only yesterday updating a new UK 1340 for it's oneoff numap guarantee. I took some screenshots because it was being offered both unicode AND non-U updates. Not home at present so i'll post them later.