It's related to my last statement, "There is no lagging for people that disappear; i.e. when Heath Slater wrestled Sid on RAW, Sid was still at his old high WWF value. "
It also means that when Backlund returned, when Steamboat returned, when Nash returned and when Golga (Tenta) returned, they retained their old ELO rating.
The reality is that it probably make sense to:
I. start driving numbers down due to inactivity (i.e. Piper vs O'Haire is a lot different than Piper vs Hogan) and
II. consider resetting numbers all together for new gimmicks (should Tensai get Albert's old numbers? What about Kane and Isaac Yankem?)
My suggestion would be something like 20-25% drop for every year not appearing.