That's really all the info you need. They are streamlining the whole high-grade (Hand made) production thing for tubas and euphs and in order to differenciate between the newer (and more exspensive when they release more pricing details) High-grade horns, they are labeling the general line 'Overture' or as LargoBone explained it, placed the general line horns such as the Dolce into a separate tier. This should also clear up your confusion about the Overture being an older gen model, which it isn't (At least for now, they are working on a prototype Euph that is estimated to be around the $3,000 range)
TLDR; Overtures are the non-handmade horns such as the Dolce, they are a tier not a seperate or older model, the handmade ones are not labled Overture as they are Higher-grade in both materials and craftsmanship, such as the new $3k Sinfonico Euphonium they are releasing later this fall.