Just before Grams dies, she places the Book of Shadows in a trunk which is to the right of the attic door. In the series pilot Phoebe finds the trunk in front of the window.
In the flashbacks Grams is worried about the girls losing their connection as sisters if they become witches which is why she plans to use the potion on them the day she dies. But the girls time traveled back to before this event and she saw they were going to be fine.
When Phoebe walks in on Piper and Leo in the shower, the bathtub has a glass door but when Prue previously walked in on Leon in the same bathroom, the tub had a curtain.
Piper finds Grams potion bottle in the trunk but in the flashback Grams was going to use the potion and had the bottle in her hand when she collapsed on the stairs. It was already established that the girls had not been in the attic before the events of the first episode so the bottle should not have been in the trunk.
Towards the end of the episode, Piper & Leo are sitting on the tailgate talking about not moving out. The camera keeps switching from side view to front view. When the camera shows the side view of Piper all her hair is pulled back from her face, but when the camera shows a front view the hair in her sideburn areas are hanging loose.
The girls did not live in the manor when Grams died. In the pilot, Prue tells Pheobe that she & Piper gave up their apartment to move back into the manor because it belonged to their family for generations. They also had to be living together before Prue got engaged to Roger because she & Piper wouldn't have moved in together right before Prue planned to move in with Roger. Also, when Piper is freaking out about the spirit board's pointer moving on its own, Prue is trying to convince her there's nothing in the attic and Piper replies "We've lived in this house for months now, and we've never been able to get that attic door open." She wouldn't say "months" only 6 months after Grams' death if they had never moved out before that. Finally, later while Prue has reconnected with Andy, she tells him that she is "living back in Grams' house" meaning she had moved out long ago and didn't consider the manor as her home, but as Grams' house.
The show's writers apparently forgot the gender of Kit the cat. Previously, Kit was female, but now Phoebe says, "You know, I don't think I'm ever gonna be able to look at Kit quite in the same way. Or get undressed in front of him, for that matter."