[Gore]

You cooked fast, so you will have a larger temperature gradient through the roast. Note that the outer edges are much more done than the interior on that second roast. The temperature throughout that roast is going to vary. And you are going by whatever temperature your probe happened to be at. Unless you are dead center, that center is going to be rarer than what you're going for. A couple of things to note. These are very small roasts. I've cooked steaks bigger than these. How long did you let these rest. Medium rare is between 130-140*. If you let these rest, covered in foil, the temp will continue to climb in the center, typically about 10* for a roast. Did you bring these up to room temp before you cooked them? You'll get a much more uniform result if you take them out of the fridge an hour beforehand to let them come up to room temperature.

That first roast is on the rare side, which is exactly what I'd expect if you took it off at IT120*. It will still be rare after the rest. The second one is a very nice medium rare. I would've expected that to be done more at IT 137*, so I'm guessing you have a thermometer placement issue with that. The last roast I did, I stuck it with two thermometers. There was a 10* difference between the two due solely to thermometer placement!