Hand Tools Archive
The purpose of the narrow cockbead on the bottom edges of drawer fronts is twofold: firstly, it doesn't weaken the area below the drawer bottom housing to the extent a full-width bead would.
Secondly, a narrow bead is less likely than a full width bead to catch the subjacent drawer divider (and be dislodged) due to divider cupping or inevitable drawer runner wear.
The exception to the above are those bottom cockbeads on bow and serpentine drawers which are full width due to the length of time it would have taken to fit narrow beads.
The top beads weren't always full width and bottom beads on straight drawers weren't always narrow, but one would have to say the norm is: Full width cockbeads on the tops of drawers, narrow beads on the bottom of straight drawers and ad hoc on the bottoms of shaped drawers.