Originally Posted by
IAmSam
This is a UN-55 in one of my bikes. Can you make out the spacer? It's there. When I first got this frame, I had the shell faced - damn thing came back 67mm wide. Like on the OP's bike the UN-55 I got for it would not snug-up all the way on the NDS. I decided to put a 1 mm spacer on the drive side. Works good for me. Hope whatever you choose to do on your bike works as well for you...
That's how I envisioned a spacer working on the OP's bike, but as @
TejanoTrackie said, doing that will affect chainline. Because your BB shell was shaved by a millimeter, the spacer had no net effect on yours, but that may not be the case with the OP's bike. Whether a millimeter of chainline makes any significant difference is a question of how straight it is to begin with.