Should "authors of suggested" be "authors have suggested"?

Looks like it's just a typo. Should have been "have"

Thanks.
From Hawking's new article. The copier was so careless then.

Or ignorant. Many people in English speaking countries write 'of' when they mean 'have', especially in phrases such as 'should have', 'would have' etc.

Do they also sound "should've" as "should of"?

Yes, this happens too.

I guess that's where "should of" came from?
The slurring of "should've"?

Contrex: Or ignorant. Many people in English speaking countries write 'of' when they mean 'have', especially in phrases such as 'should have', 'would have' etc.
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That's ignorant, Contrex.

If it was ignorance then these people would not know never say 'would/should/may/might/must/etc have'. It's a typo, a momentary confusion similar to their/there/they're and the like.