Thanks all (and sorry for delay, I only got to contacting parago/staples today). I’ll give details of my experience for future reference.
I online chatted with Parago, and after a bit of time all they could confirm is that the rebates shipped. CSR gave me the following number: 866-923-0052,(not the 2 for Spanish) press 2, press 2, which I think is Staples Rebates. There the rep confirmed that one had been used entirely on October XX in Staples City/State; and the other hadn’t been used, (the latter is the one I had in hand.) She was able to cross-reference the Rebate Tracking number (when rebates are submitted) with the Reward Tracking number (which is on back of Visa cared, and on paper sent with Visa).
After that I was actually able to find the receipt on October XX, and sure enough it had a payment line with $16.99, the amount/card I was ‘missing’.