Welcome to the forum.
The oldest code book that I have avaliable is the 1978 code. In the Notes to Table 310-16 Note #3 has the what is now Table 310.15(B)(6). The Table is basically the same as the one today but it stopped at a 200 amp service. There is a bar by this section so I don't know what change from the prior code.
Sorry I couldn't be more help, I am sure another forum member will have access to older code books.
Chris
The numbers you have in your 78 was the first time it appears in chart form the code. That's the reason for the bar. Prior to that, the sizes and amperages were listed in a sentence. "Types RH, RHH, RH, THW, and XHHW aluminum and copper-clad aluminum conductors shall be for sizes No. 2-100 Amp., No. 1-110 Amp., No. 1/0-125 Amp., Nol 2/0-150 Amp., No. 3/0-175 Amp. and No. 4/0-200 Amp."
In the 1971, the same figures are given at the bottom of Table 310.14, "Allowable Ampacities of Insualted Aluminum and Copper-Clad Aluminum Conductors".
In 1968, 3/0 was listed as good for only 170 amps. I trace those numbers back to the 1956, Chapter 10, Table 1a.