I'm guessing the dome was spliced in? Seems to fit well, and looks like a great job masking the windows (having built many 1/72 aircraft and helicopters I know the pain level)
The windows in the dome is a clear cast piece that is inserted from the inside once the roof has been painted. No masking involved. I salvaged the dome off of an old Rowa dome car and grafted it onto a Rivarossi observation car.