It's not really a "limited edition"...I mean, I suppose it is as each year is a release based on that years stocks, but to give you some perspective on numbers;
The Diageo Special Releases come out each fall (your super premiums etc) and they do a Lagavulin 12 yr old. I buy one each year as they are absolute crackers and tremendous value for money.
2012's release was "limited" numbers and a run of around 30,000 bottles (31,656 to be exact).
.....now, the DE's are no where near as limited as the 12's....so your talking dozens of thousands of bottles of each years DE.
Buy them because you like them, but dont buy them for a high return on investment....because you wont get one.
Personally for me the PX kills what I want in my Laga so I never buy the DE's
they are good whiskies, but I'd take the standard 16 or the 12 special any day of the week