44/55, 44a/55a saws and the 1-70/80 are all the same round two screw mount mufflers.
1-71/81 on up were normally a rectangular muffler, and most were affixed with three screws but I can't say exactly where the three screw mounts begin.
Some of the 250, 300, and 380 saws also came with round, two screw mount mufflers, these were the type with the band clamp.
The 33/35/39 model saws also had a two screw mounted round muffler but I think they may have been taller/wider than the multi-piece round mufflers used on many of the large frame saws.
The Super 44a IPL's show a very sophisticated multi-piece cast square shaped muffler. I am not sure if I have every actually seen one of those.
Mark