Proof Surrogate Vs Alleged Certainty

What is the difference between these two fallacies?

The proof surrogate fallacy seems to involve language that makes the claim seem certain, when it is not, with no premises provided nor evidence, like alleged certainty. Alleged certainty seems to use language, such as 'everbody knows' that could be seen as a surrogate for evidence, like proof surrogate.

I've also looked at references made in the Logically Fallacious book, and the author of Logical Reasoning writes the following:

'A proof surrogate is a less well-known rhetorical device, but we’ve all seen it. When a politician 
says, “Everyone knows there should not be this kind of tax increase,” this remark is claiming 
there’s a proof, but not giving the proof. That phrase, “Everyone knows” is a substitute for the 
proof, a “surrogate” for it. When your neighbor says, “Studies show that two to three alien 
spaceships land on Earth every year,” you spot the phrase “Studies show” as being a proof 
surrogate and realize that you shouldn’t accept the claim about alien spaceship until you get the 
proof itself.'

How do you distinguish between the two? It seems like any language that makes a claim seem certain is going to be a surrogate for evidence.

They are similar, but I would say the difference is in the language used. We can even say that Alleged Certainty is a subset of Proof Surrogate . With Alleged Certainty , there is the added element of certainty (or extreme confidence), and that statement of certainty serves as the Proof Surrogate .

It's common knowledge that aliens anally probe humans all the time!

The phrase "it's common knowledge" alleges certainty as well as serves as surrogate for evidence of these rectal-probing visitors.

The earth is flat. Google it.

"Google it" is the surrogate for the proof, but is not alleging the same kind of certainty as the previous example.

As Dr Bennett said, it's to do with language.

Proof Surrogate  asserts the truth of a statement (e.g. "The author is simply wrong"), using words - like "simply" - to surrogate as proof, when this should not be the case. It's a way to get people to accept non-proofs as evidence of an assessment.

Alleged Certainty  is an argument from omniscience, where one claims universal knowledge, then demonstrates it (e.g. "Everyone knows feminism is outdated"). You could argue that it is a subset of Proof Surrogate, since the statement of certainty is acting as proof, or even a form of Begging the Question, where the conclusion is assumed in the premise.

I see the main fallacy as Appeal to Common Sense  or Appeal to Common Belief 

The second fallacy, using "studies show" is like one I have called out on several occasions, when the preamble is "scientists say", and both are Appeal to (False/Unknown) Authority or Appeal to Trust