The radio market is all of LA County and the OC.I'm thinking that KRTH must have surveyed an audience outside of the city of Los Angeles, as big as it is. They probably had to sample the suburbs of Orange County.
Otherwise, KRTH wouldn't be playing Shania Twain and Johnny Cash. JMO
Music tests now are done, mostly, online. People are recruited to a quota, which has percentages of men, women, different age groups, ethnic group if warranted. Most important, they usually have to be heavy enough users of the station to know the music and to be able to give opinions.
For example, the specs for KRTH could be ages 34 to 49 in equal 5-year cells, 60% women, minimum 35% Hispanic, covering hot zips in the San Fernando and San Gabriel Valley area, Santa Clarita, Central LA county, Central OC, West Side, Long Beach as close to proportional as possible, listen to KRTH at least an hour a day.
The recruit is done by a professional recruiting firm who contacts people and runs through a questionnaire. If they "pass" they are invited to participate in an online "survey" of songs and they use a code to log in and grade each song based on a short hook.
Because of the use of phone recruiting and online testing, the participants will usually be sought from all the "hot ZIP codes" of the station based on ratings. Counties and ZIP codes are key. Individual cities are totally ignored as Nielsen does not measure cities, it measures markets.
I believe those two songs were played as part of a morning show feature and are not in the normal playlist. I can only find them once on one morning show date.