69 Drum Brake Master Cylinder Date Codes

[Davtona]

So on 1969 all 4 drum brake B body master cylinders how do you read the date code? The picture I attached shows the nose of a cylinder with 177 8 stamped. But I also have a cylinder with 278 4 stamped. Not sure if that 2784 is all one number or 278 4 with a space. So are they coded by the 1st 3 digits as day & 4th as year or do these go by the 10,000 day calendar?? Both cylinders look identical on the underside. So if the 1st one by day and year is 177 day of 1968 which is very possible. The 2nd one would be 278 of 1974 however. Castings are too similar for that to be correct seems to me over that many year spread. 2784 by the 10,000 day calendar would be March 12 of 1969 which makes sense also. I've got a couple more sitting around but I think this muddies the water enough to start with. These all came off cars as far as I know and were not over the counter parts.