Date: How to describe timespan?

I wonder if any of you has a good idea. I have a performance date field. Which is usually set straight forward
like this: 2020-07-02 JJJJ-MM-DD. Sometimes not a single day/date is given, but a timespan, e.g.
Nov.-Dez. 2020, 1.-3.07.2020 or 1.,2, and 4.07.2020.
Have you got any suggestions how to handle these and similar case?
2020-11 to 12, 2020-07-01-03, 2020-07-01-02,04?
Is there a standrard? A good practice?
Thank you!

The only tag fields with a date information are YEAR and RELEASETIME.
YEAR is defined as 4-digit number.
RELEASETIME apparently gets deleted from ID3V2.3 tags by some purist applications and defines a point (no span) in time down to the second.
As there are not other fields, I assume that your field is a user-defined field.
And as you as a user defined it, you can fill it with whatever you like.

So I think that one has to define what the purpose of that field should be and in what context the field's data will show its virtues. These criteria may then lead to some ideas about an appropriate format.

You are right, it is a user defined field. I use the field mainly to store the date of a performance or the recording.
But there seems to be a TRDA field: "TRDA The 'Recording dates' frame is a intended to be used as complement to the "TYER", "TDAT" and "TIME" frames. E.g. "4th-7th June, 12th June" in combination with the "TYER" frame."
That would make it a combination of YEAR and DATE. Although I would say it makes more sense with TORY/ORIGYEAR.
I just want so store the inforamtion of the performance or recording date in the file. But sometimes I use it with albums of previously unpublished songs from long a ago and extract TORY/ORIGYEAR from the performance or recording date.

Before my searches for a standard did not bring any result. Just now I found while looking for RELEASETIME the following: "The timestamp fields are based on a subset of ISO 8601. ... For durations, use the slash character as described in 8601, and for multiple non- contiguous dates, use multiple strings, if allowed by the frame definition."
But I haven?t read the ISO 8601 yet.

I see what you do. And that is up to you as you could continue to do so without anybody noticing.

But if you want to re-use the data for something, e.g. use MP3tag to filter for a certain span (e.g. "show me all festivals that took longer than 3 days") and transform the result into a playlist to be used in a player, then you would need structured data to do the calculations.
But if you enter the dates only for record keeping purposes - go ahead.

If I understand the ISO correctly a timespan is given as 2020-11/12, 2020-07-01/03 or 2020-07-01/2020-07-03 Which is fine with me, as I don't write to a filename (/).
But what would that mean: "for multiple non- contiguous dates, use multiple strings" ?
Something like that 2020-07-01/02, 2020-07-04 or would I have to write it in two tags

How could I structure the data, to achieve what you are suggesting?

Another thing, the definition for the TRDA field is not realy structured, is it?
"The 'Recording dates' frame is a intended to be used as complement to the "TYER", "TDAT" and "TIME" frames. E.g. "4th-7th June, 12th June""
That looks more like just text.

The longer I think of it:
Why don't you introduce 2 user-defined fields?
It is then up to you to develop some kind of semantics.
E.g.: Why be overly picky with

but have a

span of months ...
So in case of the July event, start date would be 01.07.2020, end date would be 04.07.2020. I would ignore the gap - unless you know that the gap is important. But then you should know which recordings happened on the first 2 days and which one after the gap. And set the dates accordingly.
in case of the nov-dec-event it would be 01.11.2020 and 31.12.2020
If you know the exact date of a recording, then you could use an exact start and end performance date.
The main purpose is: get the data unified and structured.

you are right, when I know the correct date, I can set the date per Track differently. If it is not known, than it should not matter that much. And anyway, I also have it in another Notes field as text.
For the month span, if I knew the dates I could use 2020-10-12/2020-12-15 which would be the ISO way or as you suggested a start and end field.

Thank you! I got me on the right track.