<p>A logical guess is that in the first series, before the war, the staff size was large enough that all but the senior members of staff had to double up. Through and after the war, the staff, if not the cast size, would have both been reduced and more members of staff would either come in from town or have cottages on the estate. As a result, fewer people would need to double up. </p><p>By the last series, even Andy had his own room. Presumably that would be the case with the remaining female staff as well. </p><p>As an aside, the butler would typically sleep with the silver and wine, to see to it that nothing got stolen, since it was his head if it did. DA shows his room to be up with the other male staff.  </p>