You may very well be right. I hope you do, because otherwise it would be another error made in the films. Driving a car from 1927 while it was 1923.

But I personally still think it's a 503. You can notice the difference by looking at the front fender (not sure if that's the right word) of the wheel. You see the ones on the screenshots are similar to the ones of the 503's on the pictures. The 501 however has a slightly different front fender.