I manage a store selling prescription glasses, many of which are unisex or apply to more than one category.

I have already assigned the canonical URL for each category, but my question is, if a product appears in more than one category, do I need to set the canonical URL in each product to reflect the category I want it to index under? Therefore, any additional categories that product appears in simply refers the link value back to the canonical URL.

I note that in Yoast, under each product, there's note in the canonical setting to leave it empty to default to permalink, so this has confused me a little. I'm just concerned that by applying a product to multiple categories, it may be causing duplicate content, as I have a lot of duplicate issues which I'll raise in another question.

Thanks!

Does Google differentiate between keyphrase structures such as Mens Sunglasses & Men**'**s Sunglasses? I.e. does the inclusion/exclusion of an apostrophe make any difference when optimising your main keyword/phrase for a page?

Keyword explorer appears to give different results..... I.e. no data for Men's Sunglasses, but data appears for Mens sunglasses. So if I optimise my page to include the apostrophe, will it screw the potential success for that page?

Thanks

Bob

Thank you Rob, that really helps!