https://wiki.openstreetmap.org/wiki/Key:old_name#Date_ranges

"When only ranges of years are specified (no month or other details), a single hyphen may be used, such as `old_name:1953-1990 = Ernst-Thälmann-Straße`.

When full dates are specified or the simple notation is not sufficient, a double hyphen ('--') can separate the from and to date - e.g. `amenity:1965--1971-12-18 = school`."

:/