Just because a book has the Canadian disclaimer doesn't necessarily imply that it is not in the PD in other countries, like the US. In general, all e-books uploaded to MobileRead will contain the Canadian disclaimer because MobileRead is hosted in Canada and we thus ask our uploaders to comply to Canadian laws. If you download a book, it is your task to make sure that it also complies to your local laws.
A few e-books in our database are not hosted by MobileRead (they have a different disclaimer). These are works that are in the public domain in the US (and perhaps other countries), but not in Canada.
* Wikipedia on Public Domain