I have to imagine there were some early concept documents drawn up as part of the business plan to buy the property from AEG. A little less than 2 years seems about right.
I don't think it would make business sense otherwise, even if it were only rough ideas like "an X system like Game of Thrones with the Y system from Star Wars, but with the Z from Warhammer". Zinser said that the original conversation had been about getting advice on how to save L5R, presumably by adapting it into an LCG. Someone with FFG probably started thinking about how to do it and decided that they could do a better job in house. If I were a betting man, I'd bet that the fundamentals of L5R's new system exists as a set of sticky notes on someone's wall right now.