There's no such thing as "catcher's interference" in softball.
(It's "catcher's obstruction".)
A pinch runner and a courtesy runner are two separate things, covered by separate rules. One's a substitution, the other isn't. I suppose you could say that a "player" could reach first base either way, but I don't think you could say that a "batter" reaches base that way.
We covered "catcher's obstruction", but there is another kind of obstruction that can put the batter on first base, without hitting the ball.
With a runner on third and a squeeze play on, it is possible for ANY fielder (not just the catcher) to obstruct the batter, either by preventing her from hitting the ball, or by touching the batter's person or bat. So, the batter could be obstructed by the third or first baseman charging in to play on the runner.
That would not be catcher's obstruction- it's just plain old obstruction, though only in a special set of circumstances. I would have to say that this is an exceedingly rare call, but it is a possible call, one covered by it's own specific rule in the rule book.
If that's not on the original list...then they need to add one more to the list!