“An open short position CANNOT be *LEGALLY* hidden."“
There is no “legally” qualifier required. It can’t be hidden by any means.
And that is supported by the fact that there has never been a hidden short position suddenly uncovered.
Now, sure there are nefarious players that in the past have tried various mechanisms to avoid the “consequences” of an open short, especially a naked one, and almost all of those have been eliminated…but the position it self can’t be hidden.
Try finding a single example of where that has happened. You won’t be able to.
And sorry…”people break rules” doesn’t cut it.
This particular issue isn’t about rules so much as how the reporting system actually operates.
And for those that are interested in learning more about it…here is some light reading:
Market Data 
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