Yeah, ditto quizivex and twistor here.
Plus, if fewer people take the test in April, then the confidence level for any given interval will be lower, because statistically there is less data. So it it might be easier to score higher and score lower, the normal distribution won't be as well defined. But either way, I think that there are enough Physics GRE test takers on any set day for any given test version (there are different forms on each day) that the ETS is able to be confident enough, for all practical purposes. Plus, I think, most places ignore small score differences anyway.