Originally Posted by
HillRider
You can't tell just by the lack of paint and calipers aren't really going to tell you enough as it's not just shell width but parallelism that counts. One way to check is to install the external bearing cups moderately tight and try to slide the crank spindle through them. If it lines up with both cups with no wiggling or forcing, you are good. If it requires twisting or force to get the spindle through the second cup, facing is needed.
+1 This is a great explanation the issue isn't rather the BB has been faced so much as rather will the BB and spindle align correctly. On a high quality frame it will the majority of time. In the rare case it doesn't the BB will need to have some work done at better shop that does work on vintage frames.