As long as they were properly stored and don't appear to have oxidized, there is no noticeable "disadvantage" IMO. I actually bought some old Mustad hooks just like you are describing not too long ago and tied up several different kinds of flies with them. I've caught decent sized fish on some as small as 20's with no problem. Some of the ones I acquired don't even have numbers that I can find but they work great. Hope this helps.