Why do the Dallas Mavericks have old Denver Nuggets uniforms?

When I was a little kid, I used to mistake the cities of Dallas and Denver for each other.  They were both far away, began with a "D" and the words looked alike to me.  However, the main reason for my mix-up was that I owned a yellow t-shirt of the Dallas skyline (which I think one of my parents brought back for me from a business trip, it vaguely resembled the one pictured), and the Denver Nuggets logo looked liked this:

So when I flipped on ESPN the other day and saw Dirk Nowitzki and his Mavericks teammates wearing these, it only added to my 30-year-old confusion:

Here's former Nuggets star Alex English:

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