I think that the Cepheid distances are about as accurate as our knowledge about the distance to the LMC. We have observed and studies a very large number of Cepheids there, and so the statistics about their brightness is pretty solid. Our distance measurement to the LMC is not so far off as to allow the kind of error bars you are asking about.

In about ten years when the Gaia data is in, we'll have very accurate direct trigonometric measurements of the distances of quite a few local Cepheids. This will also help nail things down.

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