When Jeffrey Dahmer comes home in uniform, he is wearing a National Defense Service Medal. This medal is only awarded during times of conflict. The Vietnam War eligibility period was January 1, 1961 - August 14, 1974, and the Gulf War period was August 2, 1990 - November 30, 1995. Dahmer served from 1979 to 1981.
Jeffrey Dahmer is shown to purchase a suitcase to transport his victim's body out of the Ambassador hotel. The suitcase is a vertical rolling suitcase with a retractable handle. These were not invented until 1 year after this murder.
In the hotel room right after waking up next to a dead Steven Tuomi and right before pulling body to the ground to do (unsuccessful) CPR, the corpse swallows.