It's hell getting old and not remembering your memory isn't as good as it once was. And I hate putting out bad info, and then George goes along not questioning. Good thing Johneeb has a picture to refer to and not rely on his memory.
The '48 with the early steel bracket came with 5 spring leafs.
The '49 170A and on used the same steel tail wheel bracket but only used 4 springs, the same 4 lower springs but not the shortest top spring found on the '48. This carried through to the B model with the steel and then the "fish mouth" mount.
My mistake was I referenced only the B model IPC as I knew it had both brackets pictured. I saw the early steel bracket with 4 springs, not remembering only the '48 had 5, subtracted 1 from 4 or one spring less and incorrectly advise only 3 springs are used in the "fish mouth" bracket. Which of course I was being told fit nicely confirming my mistake. I'm sorry, I must be much more careful.
So in short, '48 with steel bracket, 5 springs, all other years no matter the bracket type, or a '48 with "fish mouth" bracket 4 springs.
As to why 3 springs might fit nicely I can't say. I've seen springs of various thickness, perhaps 3 thicker springs might fill the space, but there should be 4.