When the original Stewie returned to present day, his return pad was missing.
The part where Stewie goes to Oxford University to get the parts for the time machine it is shown as one campus. The University of Oxford is not one campus but a collection of colleges and departments.
Stewie was reborn in the UK. Stewie is looks down at the dog licking its own snot while the doctor is holding him. There's a NEMA 5-15 (Type B) electrical outlet on the wall behind them. The UK uses the BS 1363 (Type G) electrical outlet with 3 rectangular pins.
When Stewie is reincarnated as the son of wealthy English aristocrats, his father mispronounces the word "valet" when introducing him to the household staff. British pronounce valet so that it rhymes with ballot, not ballet.