I think it's very likely my drums came from that set, as I also got helmets, breastplates, shields, trumpets and some tabards (for the figures' backs) that also appear there. This explains why the breastplates seemed so loose - they are designed to be worn with a tabard behind as well.
I now see more clearly the progression of printing on the knights. First off, no printing. Then when they started, they printed on the backs (as in the quartered fleur-de-lys and crown, and the Yellow Serpent).
I must have bought set 3329 some years ago, before they started printing on the bodies, and the three figures I still have from this set are some of the oldest in my continuous possession. I also have the same figures from the 3669 set, but with the yellow serpent printing added.
So, when the printing was possible, tabards became unnecessary, and the breastplates were beefed up around the neck to make a tighter fit.