Lisa's tablet says that Harry Nolsson "composed" the song "One", and died of a heart attack on Valentine's Day. In reality, Nolsson merely wrote the lyrics to the song. And while he really did have a heart attack on Valentine's Day 1993, he survived it, only to be killed by another heart attack on January 15th, 1994.
In one of the earliest episodes of The Simpsons is mention about Marge Simpson activities in the Jimmy Carter presidential campaign, however, in The Kid is All Right is mentioned she supported Bush and Reagan (This doesn't preclude the possibility of Marge supporting Carter in '80 and Reagan in '84).
For Marge to be able to vote in '80 or '84, she would have to be at least 48 years old, or 52 to have voted in '80.