Well I always wondered about that myself. I'm not sure what you were comparing the Bree-Casedy to, but it never sounded anything like our M7. The only similarity was the basic envelope of decay, (close). I did contact them and they seemed very nice, I did not challenge them, but personally, I suspected that they were not derived from the M7.
It is typical though of plugin convolution reverbs to capture just the decay envelope and little of the character of the reverb. This is because they must take dramatic short cuts to get them to run on an Intel platform. If you have ever heard the Sony 777 which performs convolution without the short cuts, you will know what I mean. So it is hard to be definitive.
Your discovery is very interesting to me however, I will try to duplicate it myself. I would love to put a good set of M7 IRs in the public domain, because I do think that they can be useful, and we must always be mindful that todays user looking for inexpensive reverb solutions may someday decide that they would like a more expensive solution if by good fortune they are successful in their craft.
-Casey