With Facts 1 and Q1-Q4, I was hoping we would explore a couple ideas that I think the responses touched on.  Here are some of my impressions from the comments ...

Facts 2 and Q5 (Obedient fouls Forgetful), I thought that Case 68 describes the issues pretty well.  John Allan really dove into the other details with his response examining the racing intent of both boats, if that's part of the question.

Facts 3 and Q6 (Forgetful fouls Obedient and Obedient request redress on RRS 2 basis) ..  Again, thanks to John Allan for taking the time in putting together such a comprehensive response.

Case 65 resonates with me on this question.  In Case 65, we have a boat that is Black Flagged, but continues to race and hinders a boat.  Notice it doesn't say she fouls a boat, rather she hinders a boat while apparently not breaking any Part 2 rule in the process.

Case 65 states, " A competitor who, while knowing that his boat has already been disqualified, intentionally hinders another boat clearly commits a breach of sportsmanship (see Sportsmanship and the Rules) and rule 2."

Forgetful knew she was not entered in the event, as she admitted to seeing the incomplete-entry list on the ONB the day prior .. but she went out and raced anyway and put herself into the mix at a mark, fouled Obedient and forced her to miss the rounding at the first attempt, significantly worsening her place in the race.

Case 65, though at first glance might not seem like it speaks directly to the question, appears to me to have some application and relevance.  Both boats knew they were DSQ'd in the race, but decided to continue racing.  The Black-flagged boat in Case 65 is DSQ'd by RRS 30.4 and Forgetful by RRS 75.1.   

It might be one thing to come out for the start .. start with the fleet and sail around the course, but try your best to stay out of everyone's way and not impact those who actually have an opportunity for a score better than DSQ.  It may be another thing to cover boats, press your Part 2 rights, and even foul another boat to the point they miss a mark, when you are DSQ'd from the event.

I think it's an interesting question to mull over.

So I just finished a really great online Advanced Judge Seminar and the opinion offered by those much more experienced than me was (if I understood them correctly) that both were ROW boats by the rules, the rule both broke was 14 but both would be exonerated uner 43.1(a) unless damage and it was a very small hole in the rules that didn't warrant monkeying with the rules. 
I still submit that the upwind boat sailing by the lee downwind should stay clear as an unwritten rule.

re: " And not sure how this changes A4 "

RRS A4 says that an RC shall score boats that start and finish.  Start and finish do not require entry or registration in the event. Therefore, I'm suggesting that by not scoring them if not entered or registered, it changes A4.

re: "registration" in the first use ..

oh .. OK .. I thought it might have been a typo that's why I asked. FWIW, using "entered" in the first use might be tighter as "enter" is the term used in RRS 75.1.

yellow will have hard time to convince me she was on proper course

I think the gist is that WS thinks (and I tend to agree) that COVID restrictions are the province of public health authorities and perhaps of the event venue host, not race organizing authorities. They should not be made rules as defined in RRS. 

I'd tend to look at the COVID protocols as similar to yacht club parking rules. Competitors are informed of them and asked to abide by them, and a breach could [DP] be a basis for a misconduct report. But a boat can't be protested for illegal parking or failure to wear a mask.