I recall hearing that Lange experienced issues with the 205.086 dial production (the blue "copper"/aventurine/goldstone dials) several years ago. I heard that they weren't able to make as many of these (or perhaps make them as quickly) as hoped, and so production ended up being limited. I don't know if that's why Lange limited the current 211.087 (black flecked dial) to 50 pieces, but it's the first thing that came to mind.
These aventurine dials are pretty cool. I have some older Omegas (from the 1970s) with blue aventurine dials, and they're fun to wear, quite different from a typical dial.

