Hello! https://www.openstreetmap.org/way/132394449/history has maxspeed:source = CZ:rural that was added in this edit
is maxspeed:source intentionally used instead of source:maxspeed ? See https://wiki.openstreetmap.org/wiki/Key:source:maxspeed

maxspeed:type is also sometimes used as a key for such data, see https://wiki.openstreetmap.org/wiki/Key:maxspeed:type