Neither in the release guideline https://musicbrainz.org/doc/Style/Release nor in the barcode documentation https://musicbrainz.org/doc/Barcode is described precisely what value should be put in the barcode field.
Some editors have the impression that that we should capture the numeric values printed on the sleeves under the barcode itself.
Others have the impression that a proper EAN or UPC numbers (scanned if needed) should be put in the field.
One is maybe more useful to people typing in the barcode to search, other to people scanning it (like with the android app, or in a library)
I would favor a clarification in the release guideline or barcode documentation for the sake of consistency.
We could start a vote to see what the more general opinion is, as suggested by reosarevok in Edit #32753531 - Edit release