I'm looking for some input on my 1968 Speedmaster. The movement serial number, dial, bezel, hands and case all seem correct for a reference ST145.012,(the 145.012 reference and year of production has been confirmed through an extract from the archives). However, the mystery is the case back, which shows ST 105 003.65. The case back seems correct for a 105 003.65 (stepped back and faded but still legible speedmaster logo), The case is clearly not from a reference 105.003 (it has crown guards). I have read that it was not unusually for reference numbers and serial number to not match years perfectly based on the parts available at the time of production. But to me, a three year gap in parts (a 1965 part used in 1968) seems a little wide and also the mismatch between the case and case back seems like an odd combination to come from the factory. The other possible explanation is a part swap but again it is a little odd that a part from an older watch made it into a newer watch particularly when it is a part that would have been very unlikely to be damaged. Any thoughts from the Speedmaster experts out there?