don’t know about instruments per say, but as a premier who has been at all levels below 1K since the merger in different years, I’ve noticed companions don’t always show up right after me - sometimes there are a few names between. It’s my hypothesis that while the wording of the companion benefit for upgrades insinuates that companions should be right below the status traveler, the system is programmed to put them at the bottom of the list for that status. In years my wife and I have been gold, for example, our non-status kid has been a couple of names below us, but above others. It’s just strange.

As for the split itself, I concur with the opinion that has improved over the years - non-status (or lower status) companions definitely didn’t always inherit the highest status on the original PNR after splitting, it definitely changed some time ago (at least up until the pandemic - I don’t have experience flying since March of last year).