1) Source tags are just tags in the PGN, and remain hidden in most display programs.
(Maybe <CG> could display them on a game page?)
Here's an example from a game I've recently found:
[Source "Alta Daily CA v11 N8 1859-01-09 p4 c3"]
So, just add such a tag for game submissions.
I suppose a correction slip can be used for games already in the DB, using the "other" feature.
2) After some protracted advocating and lobbying <CG> adopted the feature, so it doesn't strip out the tag. At the time there was also discussion about the conventions to use, with the intent of adding a guidance page on <CG>.
This all came to naught.
There is the Z-base "de facto" convention, which borrows heavily from Zavaratelliís bibliography of Kolisch:
Here are some more examples:
Now, I've also adopted a couple of other conventions worth noting
a) <G<nnn>> for tracking Game Number in periodicals and/or tb (tournament book).
b) <tb G<nnn> <pp>/<pp>>
This is for tournament books, where I just use tb as an abbrev. Note the double page numbers, <pp>, the first being the conventional, the second being the page number in the PDF (usually coming from ChessArch ref - or yours).
I recommend this, as it's very, very convenient to have the number to navigate directly to the game in the PDF.
c) < source1 / source2 / source3 >
I might use this when I get the PGN from <CG>=<source1>, but find a more definition source, say <Harding>, who in turn also gives the original contemporaneous source <source3>.
So, I used <CG>, but we have a chain of increasing authority.
Far more details then you might have wanted, but I find it a useful system which I'd like other chess historians to utilize.
Z-base v-04 link found in here: https://zanchess.wordpress.com/2016...