Last year, going strictly from memory here...after the proposed offering short interest shot up to a high of 1.6 million, and delivery failures on the Buy-In list climbed to over 1 million at the peak before declining with house 100 trades settling delivery failures.  

What that suggested to me was that after locating around 600K shares, that short sellers were naked on the remaining 1 million.  If I'm right on this, and assuming the supply of shares available to short is about the same as last year...then 400K leaves them well under 600K obviously.  And who knows...perhaps the available number has dropped, and 400K or so is the max available.

Clear as mud as always.