This is a conversation I have with people using Automated Starting Systems like RaceSense. The proper move would be to abandon, not General Recall as you've identified the boats. It would be reasonable to abandon for a reason affecting the fairness of the racing. Now, to your question about redress, I think it's probably a high bar to get redress. If they would have otherwise abandoned, has your score been made worse than if they did the proper signal of abandon? If yes, should they abandon the race and if they do, does that help your score? It's a grey area, but I think recognizing as a sailor that while they made the wrong signal, the race was still going to end is the healthy and happy answer. 

This is not subject to redress.  Not the least of which being, there are no finish positions to correct.
However, in interest of fairness, the proper action is for the RC to allow the race to proceed by individually calling all others OCS.  It is as patently unfair to deny a proper start to one boat as it would be to ignore one OCS.  No matter how many boats are in the class, a fair start is the sole obligation the RC has to the competitors, if the minority or majority of boats get it wrong they are not owed another chance. 

All the below assumes there is no additional rule requiring a timely hail of the OCS boats in the NOR/SI.

In a six boat class, a really good race committee should be able to identify the five OCS boats and recall them AND clear them.

Trouble determining who has cleared is what an RC that's unable to accurately make the recall could stand on. I once did the "all boats except" x-flag but was completely unable to determine which boats had cleared, especially since we didn't have a round-the-ends rule in effect. Making this call would require excellent work from the RC team and a lot of confidence, as well as some willingness to try, and then to abandon if needed. Since this was not done, it might be worth a heart-to-heart with the PRO that day. What would it take for that PRO to be able to make the call of five boats over? Do they know they can wait to hail numbers for many seconds while gathering data? Do they have a recorder onboard who is writing down everything they say? Are they running an audio recorder at the starts? Most club RC's are just not equipped to call more than say 3-4 boats OCS.

@Niko, you certainly bring up the fairness to the other boat. I assumed and didn't articulate that the reason for 5 of 6 boats being OCS was something unfair. Perhaps a late wind shift, a line that wasn't square to the wind, or some other reason caused the boats to be OCS. If it is a perfectly square line with nothing wrong, I have no issue with letting the race run. Many PROs fail to look at the line in such instances, and declaring yourself perfect with such a large percentage of the fleet OCS is often the wrong answer.