Possible Clues:

• Yours truly gets lot from the same source
• Might one offer a reference?
• Repetitive footnote abbr
• Footnote kin of op. cit
• Bibliography abbreviation
• "See above," in footnotes
• In the same place (in footnotes)
• "How much am __?": auctioneer's question
• Bibliography space saver
• "Sourced from the same material" abbr