Is there a "deadline" for registering Canon lenses? Does registration always require POP? I'm asking because I misplaced the receipt for one of my lenses! (Yes, I know, embarrassing!) I could contact the store and ask for a new one but I don't know how happy they are to print me a new receipt. It's not their responsibility if I lose it. Registration is also necessary for CPS "points" so I'm not only asking for the warranty.
Registering a lens can be done any time. It merely allows Canon to send you recall notices, and new product notices. It does not provide a warranty, and is not necessary for CPS. CPS has a different system for registering your lenses, you must list them on the CPS site.
A Bill of sale from a authorized dealer is still a requirement for warranty service. Anyone can register a lens any time. If you don't have a bill of sale, they may refuse warranty service, or more likely go by the manufacture date. They are getting picky due to non authorized ebay resellers selling items, but I haven't heard of them refusing warranty as long as there was a bill of sale, or if it was a Christmas gift from Grandma and the date of manufacture was reasonably close to the registration date.
Call that store and request a duplicate bill of sale! They should be happy to give you one.