Ok...I can think of one thing lately in some models is released also a file. unl (JCV+UNL)
The file UNL could be used to write to a memory area and then no longer serve (my think....!!!)
Could be used in some models (like yours) but currently we do not have the ability to check
Try also with the small JCV file in post #22 : Full screen small version 23.5MB for Nuvi 1390 & 14xx D3153100A.JCV
Tomorrow I try in my 13xx

Bye,bye