Correct -- Alan was not working on ATWT when Melanie and Mary Ellen were on the show.
I find the interviews are better, with less interruptions, when Alan hasn't worked with the guests. There is less of his own rambling, he's not as chummy w/ the actors and the interviews are more professional. The trade off is that sometimes he gets history wrong...but I will gladly trade that for depth and a little tea. The fans are always there to correct him -- and Alan often solicits their fact-checking prowess.