Before a pilot descends through clouds or poor visibility in search of an airport, she reviews, with herself or her co-pilot, the procedure she will use. That procedure is very specific, including minimum altitudes, tracks, directions of turn and so forth, and it is published on a document known as an approach plate. The approach plate is about 15 cm by 23 cm and comes in a spiral bound booklet between 8 and 20 mm in thickness, depending on whether you're looking at CAP1, the booklet for Nunavut or CAP4 for Ontario. We just call the booklet "the CAP."
In Canada, the CAP is republished every 56 days, but the approach for a particular airport may not change substantially in years. Usually the plate doesn't change at all from update to update, and when it does it is usually no more than a litle note somewhere, a comma, or a couple of feet of altitude here or there.
It's still important to verify that the plate is up to date, so the pilot confirms the effective date, at the bottom left corner of the plate. I've never been very impressed with this as a check, because it's not an expiry date: it's the date the plate was last revised and released for use. The entire book of plates has both an effective date and an expiry date printed on the cover, but the plate itself has only an effective date. I don't believe you would ever see an effective date on a plate that was after the effective date on the cover of the booklet. The publishers might know an approach would change as of a particular date that was in between issues of the CAP, but in that case they would issue the change as a NOTAM. I have a couple of plates in my current CAP that have handwritten amendments because of current NOTAMs.
They can't print an expiry date on the plate itself, because they don't know when the plate will be amended next. I suppose they don't print the effective date of the entire CAP on each plate, because then they would have to change each plate every issue. The American plates do have the effective date of the entire booklet (I don't know the slang name for their booklet) printed on each plate, so they may have a different printing system. The US goverenment plates also display an amendment number, such as Amdt 19B and another number that isn't explained but that appears to start with the last two digits of the year the plate was amended. Most Americans don't use these government issue approach plates: they pay more for plates from Jeppeson, a private publisher. I don't have any Jepps with me right now, and I can't remember the system they use.
You might think that the dates on the cover would suffice to identify the plates within, but the problem is that the book isn't especially useable in flight. The plates are printed both sides, and it's difficult to flip through to find the plates you want while flying. So we tear the pages out, or photocopy them, or tear the pages out of the previous expired book after verifying that the effective dates haven't changed, and that way we can have the plates for our current trip stacked up in the order we expect to need them. And there's no firm check that the effective date on the plate in my holder matches the one in the new CAP tucked away behind the seat.
My company forbids photocopies of plates, but most people do it anyway, because it works much better when you're flying. Every time a new CAP comes out, I check for revised ones, and if I'm pulling out previously made photocopies for a trip, I check them against the current CAP, but still it's a risk. Does anyone have a system that keeps the approach plates organized and accessible, yet provides positive confirmation that the plate in your holder is the current one?