I assume that you included the large investors that use a custodial solution like
Coinbase Custody or Xapo in the bolded category as well?

The coins that are stored by these custodial services are also not available for the price discovery.
Obviously, these services also store a much bigger BTC amount than the casual holders. According to
this Bloomberg article Xapo alone is storing nearly the BTC equivalent of 10 billion $ for their clients.

Probably there are also a non-negligible amount of BTC in time-locked transactions, which
can´t be sold even if the market drops 95 % tomorrow.