I Googled "cards about my waist" and surprisingly got a single solitary hit (well other than this thread). Peggy Seeger did the song on "Heading for Home" and is virtually identical to the Crooked Still version so that's likely where they got it.
http://www.peggyseeger.com/listen-buy/heading-for-home/heading-for-home-notes

One glaring difference is the twinkling at me knee verse, where Peggy's does call out "heart's blood." But there is still reference to cards around the waist.

All them cards about your waist
They'd do no good to me;
Love, don't you see my own heart's blood
Come twinkling at my knee, (2)