1999 Alan Lee Softcover Edition Question

I was recently in a marvelous used bookstore seeking the missing volumes from the 1999 softcover edition with Alan Lee covers, and I was surprised to find that though they did not have FotR (which I sought), they had multiple copies of TTT and RotK, the latter of which had some variation. My copy is like the one with the blue spine, but it seems the green is the one in the box set. Both have the same ISBN (9780618002245) and same front cover. I could not find information elsewhere about this variation so I figured I would ask here.