I was within that 15 days limit. If they say that I have to be postmarked by 12-30-2002, the purchase date was 12-15-2002 instead of 12-24-2002. It is difficult to make that kind of typo error.
I was fed up after 2 inquiries and finally I wrote:
"What is the guideline postmark based on? On the rebate form it says that we have 15 days to mail in the rebate form. It was shipped to me on Dec. 24, 2002. So it means that I have 6 days to mail in the rebate form? If I don't have a satisfactory answer, I will write a letter to the local newspaper with a copy of the rebate form."

Newspaper always work and always make copies of your receipt, UPC code, and the rebate form.
And I received the following e-mail
"Thank you for your rebate inquiry. You are a valued PGI-Verbatim consumer, so we are pleased to inform you that we have updated your record as a one-time courtesy. Your rebate submission is now valid. Please allow 4-6 weeks to receive your rebate.
However about your concern regarding guidelines on postmark date, rebate submission request must be postmarked within 15 days of purchase."
They still don't admit that they made error.
Anyway, their responses were fast. We had 3 e-mail exchanges in a few hours.
And thanks again, everybody.