1. MP didn't know who PH's customers were.
True but how would that have made any difference?
2. Those customers swore they weren't invested in pirate to PH, not to MP - more accurately, MP took PH's word that they'd said such - as MP COULD NOT verify that due to 1.
MP could not verify them even if she knew who they were. What would she have done other than ask them? You think they would lie to PH but tell the truth to MP? PH knew Patrick's methodology. If it was unsound or insufficient, that was a common mistake.
3. PH had responsibility to assess the credibility of his customers' claims not to be invested in pirate because a) They were his customers, b) MP couldn't due to 1.
And Patrick did assess the credibility of his customers. It's not like his method was a secret.
PH had either been told (or not told) by his customers that they weren't invested in pirate.
PH either did or did not do due diligence on those customers.
MP knew that PH claimed he was satisfied that his customers weren't invested in pirate.
MP's knowledge about the specific investments was limited to ONLY what PH divulged. There's no equality of information there.
There was nothing PH knew that would have changed MP's view. They agreed on the common set of facts and they both drew the same incorrect conclusion from those facts.
"Everyone knew PH was invested indirectly in pirate"
"PH didn't know he was invested in pirate"
"MP didn't know PH was invested in pirate"
It's blatantly obvious that the first of those three statements directly contradicts the last two.
If everyone was rational, this would be quite correct. But when it comes to greed, people have a rather bizarre ability to compartmentalize and isolate their knowledge. With subtly different senes of knowing, all of these were true. It's just like how every gambler knows that the odds are against them and many gamblers believe they will be the exception.
That lots of others also invested in PH also disproves your key assertion (that it was common knowledge PH was at risk to pirate exposure) - as noone who wanted pirate exposure would have invested at 1% per week.
It just shows what we all know, that a lot of people gamble stupidly. Everyone who invested in Pirate knew that what he was saying was too good to be true, yet in a sense those investors believed it.
Your key false assumption is that all people are fully rational and only hold logically consistent beliefs.