It is possible that the US terminology “low band” and “high band” actually predated the “Band I” and “Band III” terminology.
The VHF low band/high band distinction may have come from the FCC’s mid-1945 spectrum reallocation, effective1946 March 01. Whether the FCC actually used those terms, or whether they had an informal start and later became official, I don’t know.
My understanding is that the “Band I”, etc., terminology came out of the 1947 Atlantic City meeting, but if so, I can’t find it in the ITU 1947 Atlantic City Annex, available here: http://www.itu.int/en/history/Pages/Ple ... 0201000019
Very broadly, the global VHF broadcasting allocations developed at the 1947 meeting followed the FCC’s 1945 pattern.
Whilst one may find several references to early US VHF frequency allocations, the best I have seen is an article “What Ever Happened to Channel 1”, in “Radio-Electronics” for 1982 March, p.43ff, available here: http://www.americanradiohistory.com/Rad ... r_Page.htm
This article also includes the history of the US 6 MHz TV channel, which evidently goes back to the original DSB version of the RMA 441/30 standard. That is pertinent here given the original question about 625/25 System N, with its 6 MHz channel. Evidently there was some angst about departing from the 6 MHz American channel for European 625/50, resulting in the Gerber compromise 7 MHz channel.
Some of the “fine detail” remains obscure, though. For example, when was the NTSC TV standard, as developed by NTSC I in 1941, adjusted in terms of its sound carrier characteristics. Originally it was specified with ±75 kHz deviation and 100 µs pre-emphasis, the same as then used for FM broadcasting. Then it was later changed to ±25 kHz deviation and 75 µs pre-emphasis. My working hypothesis is that the two parameter changes were concurrent, and became effective with the 1946 channel assignments, but I have no supporting data. In the case of FM broadcasting, there is empirical evidence that 100 µs pre-emphasis was retained for the 42 to 50 MHz band at least up until 1945, and perhaps until the end of transmissions in this band. Again the (unsupported) working hypothesis is that 75 µs was prescribed for the 88 to 108 MHz band from the start.
Anyway, ±25 kHz deviation and 75 µs pre-emphasis were in place by the time that System N started in Argentina in 1951. I suspect that European ideas to use a 6 MHz channel for 625/25 included ±50 kHz deviation and 50 µs pre-emphasis, as derived from the Russian work and as eventually used in the Gerber standard. What was the Japanese thinking during the 525/30 vs. 625/25 and 6 MHz vs. 7 MHz channel debate is unknown, but it may be noted that whilst Japan followed NTSC precepts for TV, it chose the European 50 µs pre-emphasis number for its FM broadcasting.
Also, somewhere along the way, the NTSC nominal vision bandwidth moved up to 4.2 MHz from the 4 MHz noted in the original NTSC I documents. This seems to have happened before NTSC II determined the colour system parameters. But on the other hand, the tabulation in Wireless World 1952 August still shows 4 MHz. By deduction, it looks as if System N started with 4 MHz and moved up to 4.2 MHz to stay in step with NTSC.