The same proverb or everyday phrase can occur in several poems without constituting transcription. Repetition of an unusual, complete composition with its distinctive conclusion is much more probative.
Illustration A: Two poets independently say “the sun rose”; that is common linguistic material.
Illustration B: A rare full expression reappears together with its particular figurative conclusion; here simple coincidence is less persuasive.
An evaluation should consider both how unusual the coincidence is and how much of the structure has been reproduced.