MLS numbers permanent?

[Gabe C.]

I did a quick google/BP forum search for this, but couldn't find the answer... once an MLS number is assigned to a property, does it stick? Is it like a social security number or does it get reset to a new number the next time it's listed? I'm writing some software for myself to analyze things, and I'm curious if this is a dependable number that will stand the test of time. :)