Just wanted to share an incredibly frustrating 2 weeks. I had a lower headset bearing replaced on my external cup 44mm 1.5" 40 headset as it was a bit gritty and I was installing a new fork with an extra crown race anyways. I had a spare lower zero stack 1.5 " 40 headset assembly on my workbench, so naturally I just borrowed that bearing and everything seemed to fit good enough into my EC44 lower cup.
Until it didn't. Just the tiniest little amount of wiggle that was irritating the snot out of me, like a DU bushing that was just on its way out but still rideable.
So I swapped crown races with the original, play still there. Cranked the headset top cap to the extent that it pulled the startnut out. Play still there. Finally I dug into my stash and found a spare EC44 1.5" lower assembly. Swapped the bearing over, no more play!
Tl;dr EC44 and ZS56 1.5" cane Creek 40 lower bearings appear to be different, even though I see no documentation indicating this (I admittedly didn't look very hard after the fact)