This is a quote I received in an email from the NBME regarding recent step 1 test takers. Hope this helps for the applicants this year.
"USMLE score reports include information intended to help in the interpretation of results, including information about the mean score and standard deviation (SD) for a recent group of first-time examinees from US and Canadian medical schools. This information is only used in the text of the reports and does not affect scoring of the examination. Normally, the mean and SD are calculated using a full year's group of examinees and are updated once per year. Unfortunately, the values on the Step 1 score reports for examinees from US and Canadian schools that were reported on July 14, 2004 were based on less than a full year's group of examinees, which is inconsistent with prior years' practice. These score reports listed a mean and SD of 221 and 21. The mean and SD for a full year, which should have appeared in the text of these reports, were 217 and 23, respectively. This has been corrected for score reports released from July 21 onwards. The NBME apologizes for any confusion this may have caused."