These uncertainties in Cepheid luminosities are accounted for in Type Ia distance measurements. Particularly with Gaia we can now calibrate the luminosities of

These uncertainties in Cepheid luminosities are accounted for in Type Ia distance measurements. Particularly with Gaia we can now calibrate the luminosities of Cepheids in our galaxy using parallax observations. (Knowing this field I'm sure there are some astronomers who argue that there are still some systematic uncertainties that are not fully being accounted for, but from what I understand it's pretty hard to account for it with the Gaia results at this point.)