Changes to TZ database

Hello, I was wondering if someone with your organization could give me an estimate on how many times there have been changes to the TZ database because of countries moving their DST dates or other changes. (over any time period would be fine) I'm asking because I've been making a series of educational videos on youtube and am currently working on one on time zones. If you're interested you can see my videos here: www.youtube.com/user/CGPGrey Thank you very much for any assistance you can provide, -Grey -- C. G. P. Grey Time Management Coach & Public Speaker www.CGPGrey.com