There are numerous scenes where Andrew McCabe (Jason Sudeikis) is seen driving his MINI Cooper. Throughout the movie, the car has the current orange New York license plate, except for one scene mid-film, when the car is seen with the older blue and white design.
Hannah goes to leave in a hurry and gets in her truck. The truck has snow on the roof. When the truck passes the house, from the window there is no snow on the truck rooftop.
The portable 4-track machine does not have built-in speakers and would have needed to be hooked up to the sound system. As it was stored in a canvas bag and didn't have any audio cables connected, it should not have been able to produce any sound.
The mixing equipment in the late husband's shed, while passable for a band, was far more elaborate than would have been necessary for the music heard in the film, as (except for the "lost" song, which had a touch of piano) it was just solo acoustic guitar and solo voice.