Good observations.

I think the case with Stasiu being played by different actors isn't technically a mistake. There's a few instances where actors were switched. In an early episode Joseph Gannascoli plays Gino a bakery customer and of course later Vito. Chris's mother was played by Nancy Cassaro for one episode (when he's in the hospital after being shot) and then Marianne Leone Cooper took over the role of Joanne. In the pilot Siberia Federico played Irina and Oksana Lada played her for the rest of the series.Tony's sister, Barbara was also portrayed by two different actresses -Nicole Burdette and Danielle Di Vecchio.

It's like the two Darrins.