Here’s a little graphic outlining the various expansions. Note that the Dark Minions and The White Hand expansion symbols frequently were printed to light causing them to be hard to see with the naked eye, sometimes they were even just invisible.
Challenge Decks are neither limited (black bordered) nor unlimited (blue bordered). They are grey bordered instead. Only The Wizards (the first one) set had an unlimited edition. All other sets only had a limited edition.
When in doubt you can always check the © mark at the bottom of the card. When it’s a copyright 1996 and no expansion rune is visible, it most likely is a card from The Dark Minions
While a copyright 1997 and no visible expansion symbol, you are probably looking at a card from The White Hand.
You can also double check your card’s name in our extensive Middle Earth CCG cardlist and Priceguide on our sister site Good Look Gamer