TomD
Plywood is structurally divided into elements and panels. A shelf is an element, a trap door is a panel. Sounds as though your framed plywood piece is a panel. For panels grain orientation is to the shortest span.

So imagine you are at the job site. You want to build a little bridge. if you are forced to use plywood you absolutely want the long grain going the length of the bridge. It is an element, or a beam. But if you have two wooden spars, and the plywood is going to be nailed on as decking, you want the spars to span the gap, and you want to configure the long grain of the plywood so that it spans the gap between the spars, and you want to nail the perimeter.

Another example would be I joist. The webs should have grain oriented to span the two flanges, not to carry the longi loads of the whole joist.

Ply may come in balanced, form, like some marine or aircraft ply that uses a lot of very thin lams, the idea is that it will be ideal for panels being virtually equal in strength and stiffness, 0/90. However, even in that case there is still a major difference in grain aligned pieces or not. It is just closer to the panel ideal. Of course, when making elements, unbalanced ply, or other more biased products still, are preferred because these will require maximum capability in a single direction, where even solid wood might be necessary.