From around 1983 through 1988, Marvel and DC re-priced some of their comic books for the Canadian market.
Quite often, you'll find books with US, Canadian and UK prices all together on the front, something like this:
But a small percentage (some say as little as 5 percent, others estimate 10 percent) of issues produced by Marvel were created with dedicated Canadian prices.
(They often turn up in US collections in cities located close to the Canadian border, like Minneapolis or Chicago.)
The prices on the covers are always higher than the standard price on the cover of US issues. You can also tell Canadian issues, because they always have a bar code (UPC) at bottom left of the front cover rather than Spidey's head.
Let's stick with ASM #252 as our example. On the left is a US price and on the right is the Canadian price variant.
As a growing segment of the hobby, but still very much a niche, CGC has been slow to recognize Canadian price variants on their labels.
Some key issues have had the variants noted for quite a while, maybe three or four years now. Others are still in the field but not noted. And this is just Marvel.
DC Comics also produced Canadian price variants. These are still often NOT NOTED by CGC!
Whether that's because people haven't cared enough to submit them, or they are just too rare, is not clear.
What I see in the census is similar to newsstand (UPC bar code) and Marvel Canadian price variants. CGC breaks these out in the key issues, but not elsewhere.
The key is to look for DC Comics with different (higher) prices than their US edition versions. The word CANADIAN is also printed below the price, sometimes. (But not always!)
Here is Batman #357 to illustrate this.
There are hundreds of Canadian price variants, but you should stick to key issues for two reasons. The first is, collectors want key issues more than run books.
The second is, CGC breaks out Canadian price variants on their key issue labels.
Here are some ideas for you to look out for.
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