How fast do "old" MacBook Pros go out of stock?

How fast do MacBooks and MacBook Pros go out of stock in stores after the latest update announcements each year?

If the rumors that Apple will discontinue installing internal optical drives in their MacBook Pros, then I would want to buy the "older" model before it goes out of stock because I use the opticle drives A LOT for burning and reading physical media, and also like to have hard copy backups of expensive software so that it won't disppear like it would if the hard drive on a backup disk failed.

I think it would be unlikely they would completly discontinue including optical drives, but very plausible that they could discontinue including them in the 13-inch models of the MacBook Pro to save battery life. However, I don't want to have to pay an extra $500-$700 just to get the 15-inch model either.