Citing Newspaper Birth Announcement - Child not named.

Vangorden1, when we cite a source we are free to add any supplemental information we feel is essential or helpful.  There are several ways we might do this:

• If the citation is a simple one (a "one-layer" citation, as when you're citing a newspaper item directly) and the explanation is only one sentence, we can put both the citation and the explanation in that one sentence. After we cite the source, we simply add a semicolon and then add the explanation.
• If the citation is a complex, multi-layered one (as when we have to cite both the newspaper and the website that provided the newspaper image), then the semicolon would be the punctuation used to separate the layers of the citation. In that case, we'd likely put the explanation in a separate sentence.
• If the explanation is complicated enough to involve several sentences, then at the end of the citation to the source, we'd close that citation sentence out with a period and start a new sentence for the explanation.

Also:  If we choose to add information that is not in the source we are citing, then we need to add a citation and/or proof argument to document the assertion we're adding. In your example above, if you simply assert that this is announcement for Clarence, then anyone who reads your work will wonder (and you, at a later date after your recollection has gone cold, will likely wonder) what your evidence was to make that connection.

Vangorden1:  You won't be "adding a citation" to show how you came to the conclusion. Your citation is to the newspaper (i.e., the source you are citing). After that you simply add words of your own choosing to explain why you believe Clarence is one of the unidentified children in the newspaper announcement. Your explanation itself is not a citation--although your explanation might include a citation.

Let's dissect your two versions above:

1. Given that the birth announcement does not identify the twins by name, the part of your reference note that identifies the newspaper item should not assert that it is an announcement for "Clarence Garrison."  Your explanation should say that it is a birth announcement for unnamed twins of Mr. and Mrs. Albert Garrison.
2. Your second version, as constructed, tells us that the newspaper is "citing Commonwealth of Pennsylvania ... birth certificate number 1493680-22 (1922)." Newspaper announcements don't normally cite a source, certainly not a specific birth certificate by number. Therefore you would not add a "citing ..." phrase to your citation of the announcement.
3. Is this a situation in which you have two separate sources for this birth: (a) the newspaper announcement for unnamed twins; and (b) a Commonwealth of Pennsylvania birth certificate that specifically names Clarence?  If so, then you would create two separate citations, each in its own citation sentence. Don't put both sourcses in the same sentence. 
4. If the hypothesis at no. 3 is correct, then after you cite the newspaper itself in sentence 1, you should state that it is an announcement for unnamed children. I.e.,

"Republican, 8 June 1922, p. 13, col. 7 ..., birth announcement for unnamed twins; imaged ..."

Your sentence 2 might then say: "The male twin should be Clarence Garrison, whose birth certificate shows identical birthdate, birthplace, and parents; for the birth certificate see ...."

Well done. One wee tweak: The name of the website should also be italicized. Italics afe used for books, newspapers, websites and other "standalone" publications.