That separate survey has been done for years, essentially for the benefit of selling advertising on WMTR/WDHA, and those are probably the only two stations that will now show up when the Morristown ratings are made public. The other Morris County radio stations, like WKMB in Stirling, WGHT in Pompton Lakes, or WXMC in Parsippany haven't shown, in the recent past anyway, although WRAN in Dover did show before its demise years ago.
It is interesting, that the Morristown market, which ranks 120 by itself, is reported to have a population of only 420,000 while all of Morris County has a census population of 492,000. And the actual audience area, for WMTR/WDHA is much larger than Morris County alone. WDHA's most recent full NY market cume was 429,000.
As you know, Morris County has a high income population, currently median family income is $97,000 a year, and that helps make the area especially attractive to some advertisers, and worth it for WMTR/WDHA to have the separate survey. Years ago, WVNJ-FM (now WHTZ) dominated the local ratings in many of the wealthiest parts of North Jersey, when it was transmitting from the current WFME site in West Orange. I don't remember the numbers, but its ratings in Morris County were "impressively shocking" the first time I saw them, and, no doubt, helped sell a lot of the upscale advertising that station carried.
Also years ago, WCTC/WMGQ ordered the separate survey in Central Jersey in Middlesex/Somerset/Union, and claimed they were the only two local stations serving a market the size of Albany, New York. That embedded market is now ranked 41 with a population of 1.4-million. These days WAWZ, and WKXW also pay for the local breakouts and still appear in the publicly published ratings. Since it is a top-50 market I would assume they don't have to do a separate diary survey and PPM numbers are enough.