When really is Josh's birthday? In the movie, Josh has TWO birthdays!

In the first half of the movie, when Josh wakes up to discover he's big, he leaves the house to go to what was the amusmant fair. He then comes back to the house to tell his mother he's grown over night and tries to proves he really is Josh. He says his birthday is in NOVEMBER.

When Paul and Susan are having breakfast at Paul's apartment they're discussing Josh. The camera then zooms onto the milk carton which has a report on Josh missing. If you pause the screen, you can see clearly that it says Josh's birthday is in JANUARY. But, wait a second, I thought his birthday was in November. Is it really possible to have two birthdays?