I think the reason FFC changed Sonny's death to 1948 during production was for the same reason as we've discussed, and so to make the timeline more consistent.
Sonny, some people here anchor their belief that Sonny died in '49 to the presence of a "Dewey for President" poster on a wall when Sonny beats up Carlo. But, Thomas E. Dewey, the Republican Presidential candidate in '48, also was their candidate in '44, so the poster could be part of support for an earlier date for Sonny's death.
