It's a complicated question you ask, but the beginnings of your answer can be found here, in the ECX contracts, which are the official coffee classifications of Ethiopia:http://www.ecx.com.et/downloads/contracts/Coffee/CoffeeContracts.pdf
Each of the ECX contracts are traded separately on the exchange, and coffees with a given grade under a given contract are kept separate from each other. As you can see, in the "specialty" (grades 1 and 2) contracts, Yirgacheffe, Kochere, Wenago, etc. are kept separate from one another (in fact, there are A and B versions from each area, more on that later). Washing stations are assigned their area, and it is consistent with woreda. In the "commercial" (grades 3-UG) contracts, however, Yirgacheffe, Wenago, Kochere, and Gelana Abaya are lumped together as "Yirgacheffe".
The asterisks that demarcate the "As" and "Bs" of Yirgacheffe, Kochere, Wenago and Gelana Abaya contracts reference the "yirgacheffe flavor", however. This belies the reality that Yirgacheffe is considered both a specific geographic locale and a flavor that can exist outside that locale. Confusing? Yes. But understandable.
This all goes back to the history of washed coffees in Ethiopia. According to the old-timers I've talked to, the very first washed coffees were not produced in Ethiopia until the late 1950s. The pilot project- an experiment to see what washing coffee would be like in Ethiopia- was in Yirgacheffe. For some time, apparently, since the only washed coffees available in Ethiopia came from Yirgacheffe, "washed Ethiopian coffee" and "Yirgacheffe coffee" became synonymous. In addition, as we all know, there is a special lemon-jasmine aroma that comes from certain extraordinary coffees from this area. Turns out, this flavor characteristic (in my view, probably originating from one or more of the varieties grown there) can occur in coffees grown in nearby areas. This is known as the "Yirgacheffe taste". These coffees were often sold as "Yirgacheffe coffees".
Now, before people go getting all judgy about that, let's reflect that we do this kind of thing all the time in food. Texas Barbecue refers to a style of cooking, or a flavor, or even a particular set of ingredients; not necessarily the zip code of the place where the meat was cooked. Roma tomatoes, Lima beans, Manhattan cocktail...
Anyways, when the ECX showed up, they attempted to standardize this whole thing. There were some preexisting standards, but a lot of confusion. What you see above is their attempt. Grade 1s and 2s (called specialty because of their distinctive flavor and lack of defects) are sold by their specific geography. Less distinct coffees (grade 3 and below) from certain areas can be lumped together. Probably a good name for this would be "Yirgacheffe Style". Note that in order to be a Grade 3 Yirgacheffe A Washed coffee, it must possess the "Yirgacheffe Flavor".
To answer your question, what should you do? Here's what we did at Counter Culture to attempt to solve the problem. We respected the idea of "Yirgacheffe" as a flavor, but since it is also a specific geography, we felt we could not sell a yirgy-tasting Kochere coffee as "Yirgacheffe", even though people who loved Yirgacheffe flavor would probably love it. We therefore created a label called "Buna Ababa" ("coffee flower" in Amharic) to affix to coffees possessed of the unique Yirgacheffe flavor. We explained this on the label, and also noted the specific geographic origin of the coffee. Our goal was to get people to understand the nuance between Yirgacheffe flavor (which we called Buna Ababa) and Yirgacheffe the place.
I would definitely identify a Kochere coffee as "from Kochere", but perhaps note that it was similar to a Yirgacheffe (if indeed it had that flavor) or perhaps say it's a Yirgacheffe-style coffee to help Yirg lovers find their way to it. I happened to have dinner tonight with a friend who ONLY drinks Yirgacheffe coffee. I'd want him to be able to understand that he would be happy with the Kochere, without confusing the actual geographic origin of the coffee.