When Google patents says "also published as" it is not being precise and that is a primary cause for the confusion. As you are aware, each country has its own system of patent numbering. More fundamentally, the have their own entire patent systems. A Canadian patent number is not just a different name given to a U.S. patent. They may have the same specification and drawings, but different claims. Even if the claim wording is the same, the words are interpreted under each countries laws. The same words can lead to very different scope of claimed material. There are two more dimensions to the multiplicity of numbers. First, these are publication numbers. If the only difference is the number in the suffix, it is a different publication of the same patent. If it is a completely different number but in the same country, the spec. and drawings mat be the same but the claims are to different aspects of the invention.