MODERATOR V6 S3 Hybrid
Different Sat Nav companies (Garmin, Tom Tom etc) use different map data suppliers (Tele Atlas, Navteq).
I cant see many councils making the effort to inform Sat Nav manufacturers (that would be TOO helpful and clever!) but I'd guess perhaps Ordnance Survey report any road changes to the Satnav companys or these changes get picked up by those survey vans that drive around or by individual sat nav owners reporting road changes or map alterations to Sat Nav companies...
If sat nav users are giving you grief by driving the wrong way up your one way road you can report this: