If IB says 5 million available, then that means total among all brokers, not just through them.
EACH BROKER advertises ONLY the PPHM (or other) shares that can be sorted through HIS services. Some show a TOTAL (to be shared by all customers on either "First In First Served" or via some other rule).
Others show an individual client a MAX to Short (until total is exhausted).
If you use a professional prime broker (Account 1Mil$ or more and some (CS 5 Mil$ mini) then they will even close lending contracts to short on demand.
That is whiting the limits of what they can lend. If Institutionals and large PPHM position holders (e.g. Blackrock on Russel Exit) LOWER their PPHM positions you will see availability of lending go down. That is OVERNIGHT shorting will be limited (illegal naked shorting is intra-day and not influenced by this).
This observation is BROKER WIDE (One broker may still be able to maintain its lending program while another loses it because the underlying party lowered or closed a PPHM position).
I contacted IB and specifically asked them if the "available to short" number was just their number, or total for all brokers, and IB responded total for all brokers.
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