Does the 2nd printing of Deities and Demigods have Cthulhu? I have heard that it does, and I have also heard that it does not. Does it or not?
Actually, and technically, Yes. The second printing DOES contain those two mythos. It is every subsequent printing that does not contain them.
So, as you can see, both the first AND second printings contain them. The second printing contains a note giving credit, where the first printing does not.
You DID ask about the second printing specifically... and just because the first printing was halted AFTER being issued, this does not invalidate the fact that it was a first printing.
EDIT this is from someone who bought one of the original first prints in 1980, and got to see one of the second prints when a friend got his.
The second printing? Of the original first edition books?
As someone who owns multiple copies of both printings, I can definitively say that NO, the second printing does not have Cthulu mythos nor Melniboné mythos.