To make NIS happen, NBC had to explain to the FCC how this wouldn't be running two networks in violation of the Chain Broadcasting Act which forced RCA to sell NBC Blue in the 1940s. (I'm presuming ABC had to explain its four-network split several years earlier.) The explanation was simple: NBC would use the same AT&T line to feed both NBC and NIS, so they couldn't be on simultaneously.
Yes, NBC had to essentially make the same argument for NIS as ABC had to make for the four-network split a half-dozen years earlier. In fact, avoiding the issue made it impossible for the primary NBC network affiliate to delay the newscast if there was also a NIS affiliate in the market, unless the delay was to one of the optional time periods and the NIS station was covering that with local content:
So NBC primary could be delayed to anytime ending before :15, or to :30, but I don't recall reading or hearing of any station that did either.
I do know of a case where the ABC networks were delayed for close to a half-hour, in my hometown market of Oxnard-Ventura CA:
Information was carried live @ :00 by 1400/KQIQ (later KAAP)
FM was delayed from :15 to :30 on 104.7/KPMJ*
Entertainment was thus delayed from :30 to :55 on 1450/KVEN in order to finish airing before KQIQ joined ABC/I at the TOH*
Contemporary was delayed from :55 to :20 on 1520/KACY
*-There was one exception: KPMJ sold the 6:30-7:00am timeslot to a religious program, which forced the ABC/FM newscast to air @ 6:25 (just as KACY was finishing running the 5:55am ABC/C newscast) and KVEN took advantage of that to run the 6:30 ABC/E newscast live, which accommodated the airing of the morning Paul Harvey news in its place at 6:55. That all went away when 1590/KBBQ affiliated with NBC in 1976 and KPMJ picked up Mutual, although the arrangement with the three other ABC affiliates remained unchanged.
BTW, tvnut, that was an excellent job of condensing the history to just a few paragraphs without losing any of the relevant facts. 🙂