The only technical differences between the MCMVII UHR patterns and the regular issue MCMVII HR are:
Different relief to face dies.
EHR had 7 blows with annealing in between.
HR had 3 blows with annealing in between.
For both, annealing ended with a quick dip in dilute nitric acid to remove any "fire scale" (copper oxide) cause by heating.
For both, this acid dip removed some of the surface copper. MCMVII HR did not lose enough copper to change their color much. MCMVII EHR patterns, however, were dipped 6 times - enough to remove nearly all surface copper. This produced a noticeably pure gold yellow, rather than the more orange color of 0.900 alloy. Physical tests were performed by the Smithsonian on their EHR pattern pieces.
Curvature of either of these dies was too severe to allow any polishing except localized die repair, so surface texture changes relate more to planchet surfaces, and gradual adaptation of the dies to the mean planchet texture during use -- a completely normal physical process.