During the early days of team fortress 2 items had levels, levels were as arbitrary as they are now but they were not always a set level, most of those items were crafted how ever and destroyed or sold and levels reset.
Despite the desperation to sell these items I have kept a few, and seem to can't let go of.
Some I have sold though, One recent one was a level 34 vintage special killstreak Ubersaw
On doing so the level was reset to 10 on listing making them virtually less valuable.
While others I completely forgot that I had.