In my overview of the Federal Marvel advertisements I noted that the Stars & Rockers advertisement could be found on the rear cover of issues published between December 1984 and April 1985. I now think they may date as early as November 1984, and can confirm they appear on issues in May 1985.
There are actually two versions of the Stars & Rockers advertisement - the initial Coming Soon!  version and the subsequent Now available  version:
Stars & Rockers 
December 1984-February 1985
Stars & Rockers 
I'm quite confident in the months attributed to  as I have a number of samples to verify the date. I have fewer samples related to  but it does appear to be correct.
These advertisements are a good firm guide but may not be as absolute as I would wish. They may appear either side of December 1984-May 1985, but if they do they would outliers, certainly in the case of a June 1985 issue. November 1984 is a different case which I will address in a separate blog entry.
Having qualified my assertions so, let me go further and suggest these ads can be broken down into individual months by pairing them with the advertisements found on the inner front and inner rear covers. For example, an issue with  on the rear cover, a Prince ad on the inner front cover, and a 24 Rock Post-Cards ad on the inner rear cover is likely to be dated January 1985.
I have more of these pairings and dates to detail. I've catalogued two boxes of Federal DC comics in this regard. There's a bit more information for me to sort and process, but I'm feeling pretty good about getting this close to narrowing down the publication dates of Federal comics which don't have newsagency dates marked on them. By the time I'm done I expect to have a quite accurate guide to publication dates. I already know it won't be 100% accurate, but it should narrow the variable down to within a month or two - I hope!