Date in format YYYY-YYYY

[gskoczylas]

I have planty of mp3 files containging old recordings. Quite often date of a recording is set as range of years, for example 1989-1992 etc. MediaMonkey currently is not able to show such data correctly.

[MMFrLife]

You've had that year format in the Year/Date field of other programs, and it showed that way?
Numerical fields are typically restricted to show only numbers as "4/6/2017" (which translates to textual as 2017-4-6) or just "2017".

[gskoczylas]

I have MP3 files, downloaded from Internet, in which MM displays date as strange number, e.g. 3921. These file are described as recorded in years 1960-1961.

I suppose that this strange data (year) is such because it is defined as range of dates.

[MMFrLife]

I have MP3 files, downloaded from Internet, in which MM displays date as strange number, e.g. 3921

What site?

These file are described as recorded in years 1960-1961

So, they are just described that way (on filenames, folders) but don't, and never have, shown up that way (as range) in a numerical field?
Numerical fields don't allow any other formats than ones mentioned above. It's very restrictive by design. MM didn't design that behavior.
You can use a custom field to put the range in or just use the Album field if it is part of the Album name, anyway or just tack it to the end of it,
if it's not already.