Just check that you have exactly the same versions of the overlapping maps and there won't be any conflict. By that i mean make sure the microSD's CA/AL map is the same FID as the unit's Lifetime US Lower49 map because it then won't matter at all if you also have the US Northern border states included in your CA map in that case. [Same data = no conflict]. If there are no overlapping tiles though you can use different versions for US and CA, same with MX.