[mhh__]

How would we know it was referencing an old paper versus almost everything trivial already having a derivation somewhere?

[fwip]

One signal is to check the journal. Most reputable journals won't publish a paper claiming a new technique if it's actually trivial and well-known.

[mhh__]

The "trivial" is slightly tongue in cheek. It must be trivial, I've just shown it!