Now the "in-house" discussion is happening here? I never thought I would see that...
Okay a couple of things that have already been pointed out maybe but I'll summarize:
1 - There is no fully agreed upon definition of what "in-house" means in the industry. This is a creation of marketing departments and enthusiasts on watch forums.
2 - Contrary to the OP's earlier assertion, being "in-house" is not how things used to be. In fact it was completely the opposite. Once again, this is a marketing tool used by brands to create false exclusivity in many cases.
And the most important one:
3 - Whatever it means, a movement being "in-house" or not has zero, and I mean absolutely zero, to do with how good or bad that movement performs.
In addition, most watch people seem to forget that there is a lot of DNA sharing within the industry. Just like old Ford employees might find a job at GM, people who work for company A leave and work for company B in the watch industry as well. Or in the case of the 8500 specifically, people who used to design watch movements for company R, now design watch movements for company O. Hence there is a lot of R DNA in the current line of O movements...
Cheers, Al
PS - the number of WUS-like threads here lately is getting disturbing...