I remember reading somewhere that they both had older style beacons (CAIC report maybe?), so frequency drift may have been an issue. But shouldn't a trailhead beacon check determine if there was an issue? Or can drift happen between the time they hit the trailhead and the accident? I'd imagine that wouldn't be possible.
Not gonna lie, I do feel a bit nervous when I head out with someone sporting an older beacon. NWMC where I took my Level 1 class doesn't allow the older analog styles at all. It seems some people still prefer the analog style because that's what they're used to I guess. I've never used one before so I don't have any first hand experience.