Until a few years ago, stocks could be quoted beyond the fourth decimal. Then MVEE/MEMI issued 38 billion shares and showed no sign of stopping. Compared to CMKX, that doesn't seem like all that much, but at the time it was stunning.
As the stock price sank, the Nasdaq decided to do something about the situation. Unfortunately I can't find whatever directive they issued, but I believe they simply forbade stocks from being QUOTED beyond four decimals. I don't believe they have the authority to stop them from being TRADED beyond four decimals.
I believe the Nasdaq thought this would put a stop to excessive dilution and excessively low stock prices, but it didn't work. In reality it made it easier for trading to take place without anyone knowing at what price.
As you point out, this doesn't happen very often. As many have pointed out, CMKX is the biggest diluter of all time. At this time no one wants to buy or sell within the four decimal range. That's the law of supply and demand. The problem is that most brokerages apparently don't want to accept limit orders out to the fifth decimal.
You might try an experiment: put in a small market order to buy, and see where you're filled. We already know you'll be filled under 0.0001 if you put in a market order to sell.
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