During practice constructing poly's for use with Subdiv_beta6, it seems that Boolean union of 3 adjoining solids causes the loss of 4 edges.
The Boolean solid will not subdivide, unless the top and bottom are trimmed with 4 lines, to restore the 4 edges.

Using sBridge to join the outer two solids results in a solid which will subdivide.

Is it possible to have a Boolean union option to preserve the 4 edges?

The 3 adjoining solids are magenta.
The Boolean solid is cyan.
The Boolean solid with restored 4 edges is green, and will subdivide.
The red solid was made with sBridge, and will subdivide.

- Brian