Schroeder Reference alignment

I am looking to purchase the Mint protractor and need precise pivot to spindle and effective length dimensions.

This is for the Schroeder Reference that does not have any adjustment on effective length, (fixed head shell bolt). Also they are made to varying lengths.

Mounting schematic I have suggests pivot to spindle of 238 mm. Baerwald calculations indicate an effective length of 254.2 mm. Problem I have is measuring the arm it appears a little shorter than 254.2 effective length. I am getting a measurement of 243.75 mm from the bearing thread to centre of the allen key cartridge bolt. Adding 9.5 mm Lyra spec I get an effective length of 253.25 m. This is a mm shorter than the 254.2 suggested for 238 pivot to spindle. 

I am wondering if a number of arms have been produced the same length. So is 244.7 or 243.75 mm bearing to cartridge bolt length the same for any other Reference owners?