I didn’t see this in the search, I apologize if it is redundant.
Do you add barcodes to releases that don’t have them? I know I can’t be 100% certain it is the right barcode. If there isn’t one and the release is otherwise the same, should I add it?
The one I’m working on right now is: https://musicbrainz.org/release/9c70eb30-1734-4616-bff3-40bc459f7994
For the record, a barcode was added to the matching discogs without reference: https://www.discogs.com/release/204702-Change-Or-Die/history?diff=7&page=1
A barcode is a printed thing.
If it was printed on a removable sticker or obi then yes we can set it (maybe saying so in the annotation).
If it comes from the CD itself (by scanning its MCN) or from a separate catalogue (online or printed) then I’m not sure we should set it.
In any ways when it’s not obvious, you should write a release annotation.
Release is the same as what?
In general, if it’s not in the physical release, we should not set it, except in an explaining annotation, if it is useful.
Looking at the Discogs example of this based on cat number is tricky as it has no rear cover image. But they do have a barcode.
Trouble is, alongside are Promos with no barcode on the cover.
MB’s data started from a freedb import and nothing else - so yeah, if it was me, I’d add the barcode. Especially if you have this in hand and can see the rear cover.
I thought this physical release had no printed barcode:
If I understood the wrong meaning, take Ivan’s answer. 
The clarity that is the confusion of the English Language. 
I always go look at the History of a release to see if the original editor was watching the details, or just ancient bot like in this example.
Thank you both. I’ll add the barcode with a note.
I should have been more clear. I am working with the disc in hand. The physical medium has a barcode on the back. The MB entry doesn’t list a barcode, and “no barcode” isn’t checked.
Again, Thank you!