Greetings Joe,
It's amazing how advertising was conducted back in the pre-radio, tv, and internet days. I believe that back then 20 times was probably considered conservative advertising.
It's been my experience, that 3-7 times, get's the client looking your way and you make the conversion, the first time. It's the 8, 9, 10, & etc.... times, that has them coming back over and over.
Retaining a customer, is a never ending process of advertising, over and over and over again. Look at your retail establishments. Month after month, it's this coupon sale, and that % off sale. Only to be started all over again the next month with different coupon sales and "X" amount off bargins.
Thanks for the history lesson.
Woody Quiñones
ImpactYourArea.com