If you scroll down the web page about halfway you get to "Download previous purchases on Mac or PC "
Is/was there still an entry under iTunes for the purchase or was it completely gone from iTunes? If there is a dead link you have to delete that too for un-downloaded purchases to show.
If you are using the same AppleID for which you purchased the album originally it should re-download without charging you again. However, the re-download policy is a convenience and not a replacement for a proper backup of a computer. I personally would not trust it. If an item gets pulled by a distributor, or re-classified as a different item, a re-download is not guaranteed without repurchase.