Hi,

It's not a question of map segments but of .jpeg pictures : only 100 .jpeg pictures will be displayed with main outdoor Garmin devices (for example, one .kmz with 100 pictures or two .kmz, the first with 60 pictures, the second with 40).
Montana (and may be Monterra) is the only device which can accept 500 .jpeg pictures.

To get rid of this limitation, buy or make yourself .jnx files.