If you take a look in the comments to that article you will see there was some clarification regarding this.
HP had to release new SKUs of the products to allow for the bundling of the Premium License. They only released new SKUs of existing products for a small number of the existing switches (unfortunately this did not include the 3500yl range).
New switch models since then (such as the 3800 series) have always come with the Premium License.