It is accepted that oestrogen needs also to be present for progesterone-induced gyno. A-dex would be better than Nolva, however, since Nolva only binds to the oestrogen receptors rather than reducing oestrogen. Proviron is another alternative for the same reason: aromatase inhibiter to reduce the oestrogen. The body does apparently have pathways to produce oestrogen from deca and, in some, this is sufficient to trigger the gyno.
I have to accept the possibility that the sites I read when I was researching all came from a single, bogus source. Such is the way of the Internet.