The three adverbs: a) share the common meaning "to a greater degree or extent;
b) when used in comparing two or more things, may be either preceded or followed by the article, e.g. "a (an) yet/still/even bigger fool (than)..." and "yet/still/even a bigger fool (than)..."
The question I'm in search of the answer to is this:
Whether they all are interchangeable in any context.
To me, it would be easier to solve the problem I face by reading vivid examples of the usage.
As for the examples on the Google Books Ngram Viewer, try as I may, I cannot get the problem solved, if there is a problem.
So, I'd be extremely grateful to those who could suggest a couple of example sentences where one of the adverbs is more preferable than the others, or where one (or two) is/are the only possible option(s). Brief explanations of "why this and not that one" are most welcome.