The basic answer is no, one Saddle does not fit all Horses.
Some people use a Saddle with a Reg. QH Tree which is in-between a Semi-QH and Full QH and try to use various pads, cutback, built up, thick, thin, etc. to compensate, but to me that is like buying a size 10 shoe and using it for people that require a 9.5, 10 and 10.5 shoe size and compensate with no socks, reg. socks and thick socks.
If you are referring to English Saddles, to me that is even more complicated, they have more variables.
Sometimes one Saddle works if all the Horse are similar in shape and build, we have 11 Horse and only 4 of them can use the exact same Saddle.
May all your Trails be happy and safe ones