1997 Riviera - 3.8 Liter, L36 - 143,204 miles
Well.. a few years have gone by and it's been 34.5 months and 11,846 miles since the last coolant flush.
Had planned to flush it again in 3 years, which will be early June 2015. Am playing catch-up now since the Intake Manifold/Gasket job in 2009.
Will have a couple photos of the recover tank for comparison soon.
-Ed