I wasn't making the hand-gathered assumption for canaries, since by 1929 machine-mades were rolling out . . . but if it's only hand-gathered marbles we're talking about then I'd say it's likely that Steph haz a canary!
Wait.
On the document they distinguish between materials for opal agates and materials for canaries -- and in the bulk marbles they make the same distinction. So are they talking about two different things? Are we wrong to assume those yellowish-milkies in the Opal Agate box are canaries? Or wrong to assume they're (also) opal agates?
Milkie, canary, and opal are the ones we're uncertain about now, right? With a leaning toward the canaries being . . . well, like those yellowish ones in the opal agate box?
And . . . back in the day, the term opal was used to mean translucent -- but it did not mean the fiery orange backglow we mean by the term today. Just noting it. Having Hellmers' batch book right here . . .