Hello to anyone who reads this. While I’m not expecting actual answers at the moment, I hope that in the future, some MSN geek has what I’m looking for.
So for the past day or two, I’ve been looking at how Windows Live Messenger starting from 8.x all the way to 2012 parsed “pending requests”, or “invitations”. These were invites linked to Windows Live’s social network and contacts on there (nothing to do with Messenger, and the image below shows what they’d look like in Messenger (the second Messenger window):
I’ve tried every combination of XML to try to get these to display in my Messenger installation, but nothing seems to work. I’ve read the patent Microsoft released on FindMembership and its related AB services to see how invitations were stored, and nothing from there worked (no direct code was in the patent; just descriptions of how it worked). I’ve asked @TReKiE and he told me he had captures of the code needed to display these pending invites, but hadn’t saved what he had, and trying every combination of keywords on Google pulled up nothing useful. At this point, now I really wish Microsoft had kept their SOAP servers for these services online. 
If any expert on Messenger and/or these SOAP services stumbles across this, then it’d be appreciated if you can reply with details on how this stuff worked. And for anyone else wanting to reply with “idk”, then please don’t. That doesn’t help and it’s the most useless answer anyone could get. I’m not really serious about finding info on this, but it’s something that I think would be fun to toy around with and potentially use for something else. 