Wut? All seven signals were accounted for. Granted, the seventh showed up after Disco left for the future and was detected by the Enterprise, but it was found all the same.
I'm trying to remember season 2 as I haven't seen it since it aired..but I remember thinking a lot of things didn't make sense. 7 signals were seen by the federation before the season 2 premiere...the 7th signal is the one Spock saw in the season finale..how does this make sense?