The real issue, as I see it, with the Boris edition
of THE SECRET DOCTRINE, concerns its copyright.
The original edition of the book is in the public
domain, and can be freely distributed in print
and electronic form. The de Zirkoff edition is
copyrighted by the Theosophical Publishing House,
and permission needs to be obtained, and possible
royalties paid, for reprinting passages from it.
You have rightly identified the important issue in this day and age of
Internet. As for quoting from it for discussion, especially in a
non-commercial forum such as this, quoting is permitted under current US
Copyright laws. (Quoting of and reporting about even from un-published
works is permitted under US Copyright laws.) Only extensive copying of
passages,especially for commercial purposes would be covered under
Copyright Laws.