Tried all of the following:

ProdB

ProdB,1433

ProdB.my.dom

ProdB.my.dom,1433

AliasToProdB

AliasToProdB,1433

AliasToProdB.my.dom

AliasToProdB.my.dom,1433

Nothing works. Keep in mind, as I stated in my OP, all this works fine if I am logged into the DevC server (RDS or physically), which confirms to me that the target servers are configured identically. And, since users are not allowed to log in to servers, and they will be running queries from their desktops (via SSMS), it needs to work that way.