I also had an unknown primary.

I was told for OC, it is very rare these days not to find the primary because of the way OC moves from the Primary location to specific lymph nodes locations. They can usually map back from the nodes to the primary site.

There is a theory that an unknown oropharynx primary may no-longer exist. One of my RO's mentioned that the immune system may detect metastasis from a micro-tumor primary barely beyond in-situ and eliminate it.

I came across a MD Anderson study that drew a similar assumption, but my ENT thinks there was one but they missed it.

Another ENT at our NIH CCC said the path-lab may have screwed up on the "wide" Tonsillectomy specimen tissues and missed it!

My unknown location could not be accurately mapped from the nodes, so they had to treat several even larger "suspect primary" areas.

Due to multiple larger areas they elected to use TomoTherapy.
Now days all our Cancer Center have real time scanning Arc Therapy (Varian, Novalis RapidArc, Cyberknife, Tomo), but back then San Diego only had one realtime CTrue scanning TomoTherapy system.

Also the tonsillectomy+++ was brutal - they took everything! But, it is fine now and apparently I never snore at all anymore!

NCCN Guideline recommend these "wide" tonsillectomies for unknown primaries, but they don't mention they also cure snoring.