Yeah about the cusip, I don’t know what I was thinking, of course it wouldn’t help. 
I’ll have to nag H about discussing this with his mother. He’s not good at having discussions like that and of course it’s not my place…
Either MIL or her financial adviser MUST have the info, though. Also it occurred to me that H’s 2 brothers have already sold some of their shares, so we can find out what they did (although I’m not convinced that they would have done it the “right” way)