Honestly, it's a pain in the ass to swap the cluster out. I highly doubt that anyone moving any significant quantity of clips is going to change them out. Just because it came from a junkyard doesn't meant that it sat for a long time. Actually its quite the opposite. I doubt that there are any that have sat for more than a month. Personally, I'd be more concerned about compression than mileage. If it was a 20k motor and they changed the oil twice (which is more common than you'd think), the numbers probably won't be as good as a 40k well-maintained motor.

I heard that Jarco will go so far as get video of your clip(car) driving around the yard before they cut and ship it. Cost is higer than most, though.

Chris