Hi Cnfhbr
Which specifically attributes of Garmin Shapefiles, in your opinion, should correspond to these Polish attributes (Label2 and Label3) when you convert?
My question is why Garmin does not consider Label 2 and 3 feature as other editing Programs ?, in fact BaseCamp and Garmin devices recognize Label 2 and 3 on roads and make them visible when you mark with the pointer. I asume that Garmin could find an attribute solution on Road Addressing Attributes collection probably a new one.

I know a litle MicroGis Editor , it is a very good program, very similar to MapEdit, useful for verify purposes

Thanks again for your interest.