Areas with multi-million populations get updated maybe every few months, and might import and manually fix up data from the official sources, e.g. city planning.

Areas with tens of thousands of residents get updated on a multi-year schedule; a year-long construction related speed drop might remain in place for years after the construction ends.

Truly remote areas are batch imported from other systems, traced out from satellite images, or some such. Mountain and desert roads are rough suggestions at best.

This seems to have always been true of Google Maps.