I recall having those in elementary school from third through fifth grade. I don't remember specifically being told we had to make one for everyone in the class, but I remember thinking that was kind of the expectation. We didn't have to go around individually and deliver in full sight of everyone, we just sort of all did it at once, so everyone was mostly up and milling around and you could somewhat surreptitiously deliver them if necessary. This was good for me, because my way of letting a girl know I had a crush on her was if I made her multiple cards with candy in them. That way, if confronted, I could play it off like I'd lost track of who I'd made valentines for. I don't think it ever occurred to me that such an excuse was plausible deniability for someone getting two valentines, but hardly the three or four clearly individual ones with different messaging on them I'd delivered.
At the end of the day, you could easily tell who was more popular with the opposite sex by the amount and quality of the candy they got. That usually meant the popular kids got a pile of fun-size foil wrapped chocolates and full rolls of Sweet Tarts. If you were not popular, you usually got a small stack of Valentine cards that added up to maybe a quarter of the girls in class, many of which "To:" and "From:" fields were left empty. I'd also usually have a small handful of those chalky conversation hearts that were curiously limited to the blanks or, at most, the decidedly less amorous ones like "Groovy".