Appendix subtitles

Hello all--

I have a customization layer around the XSL stylesheets to suit our
publishing purposes. I've been working on some customizations but have
come up against a wall: appendix subtitles always get left out by the
stylesheets, and I can't figure out why. We are using only <article>s as
single documents, no chapters or books or any such thing. It seems that
the normal titlepage customization should allow the appendix subtitles
to show, but I've done that to no avail. Any advice?