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I believe my question focuses down to which is the safest path: 1. Never change file names on an established keyword landing page 2. Remove existing page and redirect to new improved landing page 3. Keep both until new one ranks as high in spite of some visitor confusion

This has been the way for ages now. As Alan said, YSE is okay, OSE is great, but nowhere can you get a full list, especially not an up-to-date one.