Hmm, not sure on the first question but regarding JVM 205 & 210 the Overdrive Channel on those amps is OD2 from the 410.
I always felt OD2 (Overdrive on 205/210) was Marshall's take on a more lower mid modern high gain voicing. Could be wrong but didn't really think that channel was based on existing Marshall amps as opposed to competing amps in the market place i.e Boogie, EVH etc... Whereas OD1 on the 410 is clearly hot rodded out 800.