I might be wrong (probably am) but my impression is that there is no entrance into the house from inside the garage. Has that been established on way or another?
I don’t know but I agree with your off the cuff assessment that there would be no door between house and garage. There is no entry door to the garage on the front or the side seen in some pics either. That would mean having to open the big door to get in. I think there are some pics that show the interior wall of the garage that abuts the house but I don’t recall if there was a door into the house. My memory says ‘no.’