Along with the comments above, some other things you would have to take into account are how the fish was processed in the first place- quickly and cleanly or "better get that sucker frozen before it goes bad".
At what temperature has it been frozen at: big difference in shelf life over that amount of time between -10 degrees and +10 degrees. Any power outages over that period?http://seagrant.uaf.edu/bookstore/pubs/ASG-30.pdf
This is an article showing relationships of time to temp for the time it's on the boat or on ice. A bit in depth, but if you go down to page 4, table 2, you have a list of fish including 6 or 7 different salmons (LUCC was asking what kind probably because of the differences shown) and how long the max shelf lives are based on their assumptions, including:
"Assumes fish were chilled immediately, handled gently, and held under clean conditions at each step of harvesting, processing, shipping, and display."
So, while this article doesn't talk about vacuum storage and much lower temperatures of a freezer, it does give you a relative guideline by type of salmon you might be able to use.
I've used fish up to a couple of years old that were either frozen in a bag of water (works with dove too- the sealers tend to make the cut/snapped wing bones go through the bags unless I'm real careful) so no air issues causing freezer burn, and some about a year old with a sealer. All still had that "fresh" smell unless the bag got stuck somehow and air got in there.