Was it top-3 as in hardest ones to find in high grade, or top-3 as in the most significant Sgt. Rock prototypes? (I think you mean the former, right?)
Yes definitely the former. He said something like 'these are the 3 top Sgt.Rock prototypes i have had trouble finding/acquiring in high grade.'
You can search back to the time you're looking for.
Just adjust the two search periods. The search periods cannot be longer than a year, but, you can wiggle them to find what you need.
You can put "older than" 4 years, "newer than" 5 years. Then search. Nothing? Try 5 and 6.