Yea it sounds like they are picking their favorite speaker from each cab, and going from there. This is something that again, the internet idiots don’t ever talk about: at the end of the day, speakers are a lottery. They really are. Most of us all know that 4 speakers in the same cab are all going to sound different, sometimes vastly so. And this is a great standard practice everyone should adopt before recording anything: dead center mic each speaker in your cab with a single 57, and see which one’s timber/tonality you like the best for a specific song, mix, record, whatever. I know for instance, that the bottom right speaker in my Mesa traditional rips HARD, especially compared to the other 3 V30s. I know that the older Marshall celestion vintage speakers from 1992 I just bought are much more forgiving with micing than the newer ones, and again all 4 sound VERY different. This is kind of my new rabbit hole I’m going down, constantly buying and flipping speakers, all V30s/Marshall vintage mostly, and picking the ones I like the best. Because it’s really a crapshoot. 9 times out of 10 when people compare company A’s IR of. Mesa or Marshall cab vs company B’s Mesa and Marshall cab IR’s, they are generally hearing that they like one speaker better than the other: not necessarily that the capture or mic position was wrong. So yes, there are tons of Mesa IR’s out there, as well as Marshall IR’s: but the speakers are all vastly different, always. Trying different IR’s of the same cab/speaker from different company’s is akin to what I’m doing, just in the digital world. My point is, while it costs money, I would try out as many IR’s as you can ( if you are an IR guy) even of the same cab, because they will be totally different just by the nature of speakers being a lottery in the first place.