I have no idea what Win 8.1 says about this SD card, but I can tell you Win 7 reads it as a 8GB card. Of course, all SD cards have a portion reserved for the bits that make it possible for the card to communicate with the computer and vice versa, so the card will not show the full 8GB as free for use. Possibly 8.1 is reading it as 7.1 GB, and someone mistakenly saw that as 71 MB. Otherwise, there is no way to explain the vast differences.
You must be kidding !!! If you bought it from me, it's lifetime. If you bought it from someone else, the warranty ends as soon as you receive it. However I have used several, and never had a problem with any of their cards, so I would not worry about the warranty on a $5.oo Item.. I hope this has been helpful.