Two things compound here. First, the age of the housing stock means openings vary more than they would in a newer subdivision built to one plan. Second, the winters are hard enough, in this severe cold band, that any gap in the door's seal or any flex in an undersized track shows up fast as ice buildup at the bottom seal or a door that binds when the steel contracts.
A door that was fine in October can bind by January if the track wasn't set with cold-weather clearance in mind. We see this most on homes where a door was swapped out without re-checking the track plumb against the original 1960s-era jamb, which has usually shifted some over the decades.
The honest limit here: we work out of Stamford, about 11 miles from Westport, so this isn't a walk-in showroom relationship - it's a scheduled visit, measured and ordered before the crew comes out. That means a custom-size door for an older opening takes lead time we don't control. We'd rather tell you that now than promise a date we can't keep.