Is This An Error? 2006 Colorado Quarter

First,

Just a few thoughts for discussion.
Glue or equivalent would be raised on the reverse, rather than recessed, and would not affect the strike quality on the obverse. The shadows in the photos match a recessed area.
I agree that post-strike damage should have weakened or obliterated the detail in the affected area.
A struck-through error should either have resulted in a raised piece of metal on the reverse with a full strike on the obverse or sharply weakened the reverse design appearing on the additional material if the additional metal was not retained. Even if the material was grease or cloth, the design in the affected area should much weaker than the surrounding area. Nothing appears to be retained, as the affected area shows the same color as the surrounding Nickel layer.
A lamination seems odd for a CNC coin, but could explain the detail in the struck area but not necessarily the weakness on the obverse. I would sure like to see a high resolution shot of the edge of the recessed area.
A damaged planchet possibly could explain both the detail and obverse weakness.

This is the best I could do to enhance the two photos posted by @thecraftybull.




One thing interests me above and to the left of the recessed area. There is either a jagged post-strike scratch from 12 o'clock straight to the left or there is evidence of a different process during the strike. I cannot enlarge and sharpen that area enough to get a feel for what happened there.

Just some thoughts to feed into the discussion.

Interesting coin!

Note sure what they used to alter this, but the arrows show the flattened out area. They may have used a piece of wood and hit it with a hammer. If the would was not square, but splintered, it would make an uneven affect on the obverse, while make an incuse mark on the reverse. The flatness of arrows area looks like it was perhaps done on a piece of smooth iron like on an anvil. That is the only thing I could think of that would have a shape like that incuse mark? It was tough finding that area on the an overlay. I had to create the overlay and then move it back after rotating and flipping the obverse image back to normal.