Just thinking out loud here: Assuming the 2.5mm spacers are to fit a 68mm BB to a crankset designed for frames with 73mm BB shells? Does your crank fit the BB if there were no spacers? Does the frame have a 73mm BB shell? Just because both spacers were stacked on the NDS, does that necessarily mean the crank isn't centered relative to the frame? Do some manufacturers advise the user to place the spacers that way when fitting cranks made for 73mm BB shells to frames with 68mm BB shells?