Based on what CIC says on their site, it is valid. With CIC, the best thing to do is not to try and apply one's own good sense but follow their requirements and regulations exactly as stated. As they do not talk about the expiry date of the document, it implies that this document is valid indefinitely, as far as CIC is concerned. If we were to forcefully apply common sense, that makes sense as well because if one hasn't visited a country after getting PCC from them, one couldn't possibly have committed any criminal activities in that country at least.