
The only evidence I can supply is circumstantial, but I offer two circumstances where I believe this has happened to me.
1. I was farming the 2H recipe for a while with a full backpack. Long enough for me to expect it to drop before I realised. I then made space in my backpack and continued to farm. For months. And months. Neither 1H or 2H recipe dropped. I raised the issue on here, not as a bug but a general comment in a discussion. Within a few days both the 1H and 2H recipes dropped.
2. I have been farming the last recipe I want, critical strike, for quite some time, but did realise at some point early on that foolishly I had a full backpack again. I have well over 100 Iron Basilisk Eyes and would expect it to have dropped by now.
Of course, I realise that I could just be very unlucky, so no need for anyone to pipe up with that nugget, but if a dev could confirm one way or the other that would be great.