It's apparent from my limited collection of valentine cards that my classmates and I did not have a large selection from which to choose. I don't know if you've looked at the valentine aisle at the drugstore lately, but every toy, teen idol and movie has at least one set of branded valentines. When I was a kid, valentines were mostly generic, with one exception that I'll be posting later in the week.
Here are three different cards that were obviously from the same set:
This one had a die-cut, folded part that was designed to allow you to stand the card up. The card stock is pretty flimsy, but it does actually work.
The only possible reason I can see for the big crease on this card is that it's larger than most of the valentines in the set, so it probably needed to be folded to fit in the envelope.
The valentine copywriters, as much as they clearly enjoy a good pun, were apparently at a loss with the dog cards. Doggone it.