Yes, as you mentioned, NSAIDs are highly problematic for a...

Yes, as you mentioned, NSAIDs are highly problematic for a variety of reasons, one of which is the high dropout rate from clinical trials for those who receive NSAIDs, due to the adverse effects. However, I think PAR restricts any non-iPPS treatment you can receive only to rescue therapy (acetaminophen/paracetamol or topical analgesics), so excludes use of any other treatment possibly for reasons you've stated. PAR also have a list of other inclusion or exclusion criteria that may skew recruitment away from those with a NRS of 7 or more and towards those with a NRS of 4-6.

If we break down the criteria I included in the post, it says "Willing to stop treatment with oral and topical NSAIDs, and all other systemic pain medications (except acetaminophen/paracetamol per rescue protocol) from 2 weeks before Day 1 to end of study". With this in mind, will individuals with a NRS score of 7 or more be willing to stop all treatments for 6 months? I agree with you that most may be willing to stop treatment for 2 weeks, but few IMO will be willing to do so for 6 months.

There is also a number of clinical trials with similar inclusion / exclusion criteria, results for which show recruitment was skewed towards the lower end of the pain scale. https://clinicaltrials.gov/ct2/results?cond=Osteoarthritis&recrs=e&age_v=&gndr=&type=&rslt=With&Search=Apply. You may have to look manually at some of the results to get an idea of the skew, some of these results may be relevant, while some are probably less relevant.