Any annotated screenshots you can make to help me would be appreciated. You will need to upload images to an external file sharing site, like dropbox, and share the link(s) with me.

In the form UI, for the field set up of the Post Meta for the ACF Custom Field, did you set the source to be manual (where you can manually arrange the values)?

In the database, they do or do not have these labels stored? Or, are the labels stored only in the Form UI manual entry? The 4th screenshot suggests that they are only stored in the Form UI, which is why they cannot be sorted by label.

With ACF, certain field types can have both value and label defined, in the Field group field definitions. See this as an example:

https://www.screencast.com/t/QRjopEV2kBUs

Indeed, the only entry in the actual WordPress database, in the postmeta table, are the 01-17 type entries, as they are stored as the plain text fields. Thus that is all you can use for that sort.

The list is also very long. That will cause the search to be very slow, as Search and Filter has to build that long list and perform counts on it. Having a really long list like this would not be a good end user experience.

Do these represent years and months?

Do you have a lot of posts already?

It would be better to have one field with year, and another field with edition. That way the number of choices would massively reduced and be much easier to use in the front end.

But, that would require restructuring of the data. Probably by means of a SQL command to add the extra fields based on the existing field.

This would probably require the assistance of a third party coder.