Joe-
I looked up the '37, '43, '46, '49, '50, '51, '52, and '56 codes. Looks like the change you're thinking of went into effect with the 1950 ed. The war years clearly had an impact on welding and materials technology. in '37, the max allowable SE (double V welds) was 8 ksi. The 1943 ed looks more like the material tables we're used to, with an allowable stress for SA212-B at temps not exceeding 650° of 17.5 ksi. The 1946 ed brings the allowable back down to 14 ksi and this is continued to the 1949 ed. The 1950 ed kicks the allowable stress back to the 17.5 ksi.
SweetDewMe-
Depending on service history, SA212-B material can be worked relatively easily. Unless it is in some degrading environment like a high hydrogen partial pressure, there should be no issues welding to the material. As others have pointed out, tell Compress you're using SA515-70 or 516-70 with pre-98 allowable stresses and the design should come out just fine.
Christine-
Another source is the ASTM Subject Index which states: A 212 Discontinued 1967. Specification for High Tensile Strength Carbon Silicon Steel Plates for Boilers and Other Pressure Vessels. Replaced by A 515, A516. So both the A515 and A516 series steels replaced the 212 series. From my perspective, the 516 series is used nearly exclusively vs the 515 option. In fact, I don't recall ever working a 515 vessel, might have seen one or two once upon a time...
jt