According to the family tree shown in 'Pardon My Past' and 'Baby's First Demon', the Charmed One's grandfather is called Jack Halliwell, but in this episode, his name is Allen Halliwell.
When Paige goes back to the past she is wearing a black turtleneck. When Penny and Alan convince her to go to the drum circle she is still wearing the same outfit. They are shown leaving right away without her changing her clothes, yet when they are in the park suddenly she is wearing different clothes.
Phoebe tells Paige that Paige's Chinese Zodiac is the Ox. This would mean Paige was born in 1973. Paige is younger than Phoebe, Phoebe was born in 1975. Paige was born in 1977, which would make her Chinese Zodiac the Snake. Piper would actually be an Ox.
Also on the family tree, 'Jack Halliwell's' death date is listed as 1964, but according to this episode, he died January 1967.
When Grams emerges from the door to the basement, a painted yellow wall and another door can be seen directly behind her. But as shown earlier in this episode and in many other Charmed episodes, the door to the basement leads directly to a staircase, and nothing else.
When Paige is in the living room watching Leo performing magical tricks, the song playing in the background is Rare Earth's version of "Get Ready". However, that song wasn't recorded until 1970, a good three years after the time frame for this story.
In this episode Paige is sent back to the year 1967, where she meets a really young "grams" Penny Halliwell. Penny claims to have a baby, Patty, the mother of the charmed ones. But, according to other episodes, Prue was born in 1970, so unless Patty Halliwell became a mother herself at the age of 3 or 4, she could not have been a baby in 1967.
Once Paige vanquishes Robin in the past, Grams's future is immediately affected and she turns back into a flower child. Every other character remains unchanged, although their lives all would have been significantly different if Grams had raised them in her hippie state.
The warlock Nigel is seen to have the power to freeze all activity in a room. At the end of the episode, Nigel knocks Allen to the floor using his powers, then freezes the room to kill Penny. Somehow Allen isn't frozen, and is able to get up and save her life.
When Phoebe is summoning Penny's spirit, she says the spell wrong. Instead of, "come to me, I summon thee, cross now the great divide," she says, "come to thee, I summon thee, cross now the great divide,"