There is a cycle but logic tells you the numbers have to be diminishing.
There were only so many made to start with. Some sets will have been lost or destroyed.
Some people will never sell their childhood toys and memories for a quick dollar, and many of those that will probably have.
The most likely time for people to sell their toys is when they leave their parents' home, maybe for college, maybe permanently. Age, what, 18 to 25? So a toy you have age 10 would be sold 8-15 years later. Thus a 1995 toy would most likely be sold by 2010...