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It is a really, really good idea to be able to document that the package was received, when it was received, and by whom.
Also, keep a copy of everything that you sent.
I have never lost an item in the mail, and I'd imagine you're fine in this case, so I wouldn't sweat it. The CSSA recommends that PAL's get sent in for renewal nine months in advance. I send mine in six months before expiration, and despite my track record of zero losses in the mail, always pay extra to get a signature. It's worth the peace of mind for me as I don't want to be unlicensed for one second.
1 stamp, and did yo know that there is no monetary value printed on stamps anymore. Whatever you bought that stamp for ( .55c etc) is what you will pay even if it does go up.