When my wife bought a new computer last year, the store and the manufacturer were both offering rebates. I couldn't believe how much paperwork was involved in applying for those rebates, however. She had to submit a proof of purchase label from the computer box itself, plus a copy of the store receipt and a special proof of purchase form containing a code.
If any of these items were missing from the rebate application, there would be no rebate. I can understand why companies want a definitive proof of purchase receipt to prevent fraudulent rebate claims, but it's human nature to lose a few pieces of paper once in a while. Fortunately, we did find the missing store receipt and she did get her rebate eventually.