In the first Friday after work scene, when Troy and Jim Bono share a bottle of gin, the amount of gin ranges from nearly full to half-full to three quarters empty, depending on the camera angle.
In the opening scene the trash truck goes around the same corner twice in a row as evidenced by the same buildings and the same other vehicles on the street parked and driving In the same places both times.
While sharing the pint of gin the first Friday night, the label on the bottle keeps changing direction while Troy has it on the table next to him.
This was set in the 1950s, but in the kitchen there were 3-prong outlets. Those outlets didn't become standard until the 1960s.
Cory's Marine uniform is a "formal uniform" which must be purchased by enlisted men for only formal events. Marines are issued "Class A" uniforms to wear off-base, which are a dull olive drab color, which Cory most likely would have worn.
Since Cory's varsity jacket has 1956 on the back, he must have been referring to 1955 as "last baseball season". He mentioned that Sandy Koufax led the league in strikeouts. In fact, Koufax was a rookie in 1955, appeared in only a few games, and struck out only 30 batters. He didn't become a dominating pitcher until 1961, when he led the National League in strikeouts for the first time.
A store sign had a phone number shown as 412-nnn-nnnn. In 1956 phone numbers would not have been all-numeric (instead, they would have been something like EXbrook 7-1234), nor would they have had area codes as Direct Distance Dialing was not yet commonly used and most local calls would have been dialed with only the 7-character phone number - hence no need to show an area code.
When Cory appears in 1962 in his Marine Corps dress blues, he has the Vietnam Service Ribbon, not established until 1965.
When Troy and Bono are talking in 1956, a tan 1955 Pontiac Chieftain two-door is parked at the curb. It has Buick Wildcat wheels from 1961.