Replica/Facsimile decks can list BOTH the date when the copy was printed AND the date of the deck it is a copy of. This can be done in the format of '<original date> <copy date>'. For example, '1804 2004'. This should be reserved for exact or near replicas, not inspired by decks.
In addition, for decks that were printed over multiple years, but didn't update copyright date this was useful to list it as '1970-1976' for example.
It seems the new system restricts to just 4 characters. However, at least it doesn't enforce type and allows for the 'x' designation. Please keep this:
* If the exact year is not known, common for vintage decks, substitute 'X' as needed. For example, a deck known to be printed sometime in the 1960s could be listed as '196X'.
On a related note, perhaps this is better corrected through adding a new feature instead. We previously kept a 'vintage' deck category and talked about adding a 'replica' one (although differences exist between a replica and facsimile and inspired by, but that's another finer point). Perhaps instead add a checkbox called 'Replica / Facsimile' that can be selected as needed and when selected a new 'original deck date' field appears. Then, have a view/filter called 'vintage decks' that will show all decks 20 years or older by selecting for when date OR original deck date is older than 20 years.
EDIT - this should be available for entire database view/search and within a person's collection.