You should cite the posts and resources you've mentioned, because there are a variety of caveats that approximately all the posts on WSB misinterpret. People will fly by a comment like this and just repeat it without any fact checking.

The very page you describe specifically states that you can't infer when failures to deliver occurred because the data is reported in aggregate with no age statistics. [1]

Moreover failures to deliver can occur on both the long and short side, and do not necessarily represent that a naked short sale occurred. [2] And when they are associated with a naked short sale, it may still be legitimate. Market makers are legally allowed to engage in naked short sales to facilitate liquidity, and if they can't fulfill the borrow in time (which would itself happen for legitimate reasons), that failure to deliver would also be reported.

Finally - reporting an increase in apparent naked sales to the SEC by gesturing towards data on the SEC website doesn't make sense. The SEC is definitionally aware of it. There may not be an active investigation, but these kinds of datapulls are pretty manual and staffed by people familiar with the data.

1. https://www.sec.gov/data/foiadocsfailsdatahtm

2. https://www.sec.gov/investor/pubs/regsho.htm