@Tax2019Pay , yes, if 500 purchased at Broker A, 75 purchased at Broker B, then 500 sold at Broker A, then the loss calculated on the 1st 75 shares purchased at Broker A is disallowed - the rule is to use the oldest lot when multiple lots are involved.
the washsale rule has to do with ownership, and has nothing to do with the number of brokers the shares are placed at.
that disallowed loss recoreded at Broker A can be used to increase the cost basis of the 75 shares held at Broker B.
