Michael,
Your question presented NBA's experts in tactile graphics with quite a challenge!
In GSTG 2022, section 5.2 provides us with an order in which information is to be presented to readers. The order of information is:
Heading, Caption, T-note, Key, Graphic, Source.
So, from 5.2 we are told that source information is to be placed after the TG itself.
Next, because you are addressing TGs within a braille volume and not in a supplement, for more information about how to format the source citation, we look to Braille Formats for guidance.
BF section 9.5 addresses "Source Citations and Permission to Copy." 9.5.1b is the important part for your issue!
9.5.1b: "Location of the source citation is in the fifth cell to the right of the beginning of the previous line. At least one line of the source citation must be on the same page as the material to which it applies."
There is no guideline indicating that a blank line should be placed before the source material, but we conclude that this would be advisable if it can be made to work with BF 9.5.1.
In other words,
- add a blank line before the source citation for a TG if you can ensure at least one line of the citation will occur on the same page as the TG to which it applies.
- If you can't keep at least one line of the citation on the same page as the TG, then omit the blank line.
As above, keep margins for the source citation five cells to the right of the beginning of the previous line.
Overall, our TG experts indicate that consistency in application is of primary importance. The blank line between a TG and source citation is advisable but not required. Whatever you do, keep consistent so that readers experience consistency throughout your transcription.
We hope this answers all of your questions!