In my experience any thing is a possibility when you don't mill the grain yourself. I will say that the 90/- and the wee heavy grain bill were milled at the same time by the same LHBS.
My recipe was almost identical to what you described for a scotch ale. In fact both of the brews in the last two days were identical in process, up to the mash temp. It really doesn't make sense that I would have such a change in efficiency due to the mash temp, actually I am almost ready to rule it out but there is no other difference to speak of other than temp.
In the end I boiled down approximately 2 gallons of wort from 1.055, down to 1.10 or there abouts. Adding the remaining boil to the wort previously collected I got the OG up to 1.067....still low, but I gotta just let it be. No use crying over spilt wort.
Kinda ticks me off though. Oh well time to bust open an Arrogant bastard I think and just chill out and let nature take it's course.
Oh one other thing of note with this brew. I christened my new Immersion chiller. My old one worked. Took almost 35 minutes to get to pitching temp but my new one (1/2" 50' copper) Took less than 7 minutes to get to 90 and within another 5 it was at 70. Super stoked about the chiller working like a charm.