Ross, Inc operated in a factory in Chanute, Kansas The company produced several models of guitar amplifiers, bass amplifiers, organ amplifiers, Guitars, Basses, and keyboards and P. As a result, CCR concerts were superior in sound quality, but the cost of transporting the equipment made touring a money losing deal for the band.
The first of the three digits tells us the last digit of the year (unfortunately not decade specific) and the last two numbers tell us the week.