zer I stumbitted the question, inadvertently, before finishing, so some of the info you ask may have been missing when you replied. In any case, thank you!

As I will with the suggestion from jdporter (above), I'll explore yours, as my quick test seems to suggest a way to simplify my code, greatly (the size, length of what exists is why the OP does not have a great deal of code since it's merely routine cgi- and hash-handling techniques which are well known).

in the html form, action invokes confirm.pl, and submit POSTs the sample row and 600+ others, plus some other stuff. confirm.pl undertakes to delete the items for which there is no quantity (ie, not ordered today) and the other processing I mentioned, and then creates -- dynamically, I suppose one could say -- a new (shorter!) page which the customer can review and approve (in which case, another script ships off the order, a confirmation email, etc) or revise (eg, if ordered 100 but intended to order 500 of item In.}

Hope to build a decent way to add items, too, but that's a mere glimmering. For now, the vendor will be happy with a site that says (implicitly), "If you missed an item, send the rest and then go back to go to send another order."