Also, even after Ringo and others put Ludwig on top of the sales heap, Slingerland continued to sell more drums than Rogers, Gretsch, or Camco. Slingerland was the number one selling brand for 30 years and the second best selling for the next 20 years before bad management decisions and other factors put them out of business. 50 years of high sales and production means there are a lot of Slingerland drums out there. With their early dominance (thanks to Krupa) it may well be that Slingerland sold more drums in total than any other company up until the time they stopped operations.
The later 1990's Slingerlands made in Nashville under Gibson's ownership were arguably among the best made "major brand" USA drums ever offered for sale. Unfortunately extremely high prices and very limited distribution and marketing doomed that endeavor. Gibson then moved production out of Nashville and, under different management, the quality suffered. They continued to make poor decisions related to the brand and managed to run it into the ground. They still own the name though although Gibson seems determined not to make any good use of it.