Do You Track Catalogue Values For Your Stamps?

As I organize the stamps I am focusing on (e.g., US, Europe), I put them in glassine envelopes with a sticker than indicates various information including price. I started checking the value after winning collections by auction to determine how accurate my estimate was and also to set a value for when I eventually re-sell the stamps I don't want. I like to keep track of the percentage of CV I pay for an auction. I normally won't pay more than 10% of CV for used stamps in a collection. So, I catalog the value of the separate collections I purchase. Then its just an additional step to also record the price for each stamp or set on the envelope. But I can see that updating stamp values as time progresses is going to be a problem.