I would say no. Depending on where you pre-order, you get charged at different times for those pre-orders.
If you preorder something at BBTS, you're charged when the item comes in stock as pre-orders can be changed or even canceled (ask anyone that had the First Edition Prime figures on preorder there). So, with BBTS, you don't technically own the item until they get it in stock.
Let's say you pre-order (on July 3, 2012) something with a hard release date, like a BBTS-exclusive that they know will be in stock on September 15, 2012. Since you're not charged until they actually get it in stock, September 15 would be the date of purchase (as well as the release date) as you can't buy something that doesn't exist yet.
Now, with something with no hard release date, let's consider this overly-complicated scenario.
You pre-order something at BBTS on February 25, 2012 that is in an upcoming wave that they estimate will be in stock June 2012.
The item in question ends up being released June 4th (let's say that it was spotted at a Walmart in Tuscaloosa), so June 4th is the release date that we have in the system.
BBTS eventually gets their stock in June 15th, and since you kept your preorder with BBTS, the actual date of your purchase is June 15th, even though you pre-ordered back in February.
Now, other places will charge you for the pre-order upfront, so with these stores, even though you were charged for it in advance, you don't own it until it has been officially released, again as pre-orders can be canceled at any time.
So, I'm sticking with the official release date as allowing "pre-order" dates throws off "present-time" completion percentages, the number of people that actually own the item in question, the top collectors for the category the item is in, eBay appraisal data (values and dates) and so on.
MIKE
engledogg