Would a 2006 Monte Carlo trunk lid fit a 2001 Monte?

 

I am pretty sure (90% certain) they are interchangeable.

 

I don't know but I thought the only differences were the front clip - hood, headlamps, fenders and front fascia (and the V8 !). Seems unlikely that they would redesign the body/trunklid/doors for a two year run, or only run for two years if they did. The trunk weatherstrip part number is the same for all years, if that means anything. (and discontinued - grab a used one if you see a good one).

A somewhat related question - is the whaletail sploiler held in place by adhesive in addition to the four visible nuts/bolts? I want to buy the trunk lid from a 2000 SS but don't want to pay for that spoiler and it wouldn't budge after I removed the nuts. The paint is good and not hail damaged like mine.

 

So, the 2000-2007 Monte by GM standard is all 6th gen. Under the body panels much of it is near identical. Enthusiasts refer to the 06-07 as a "unofficial" 7th gen. Primarily because not just is the interior and exterior updated, but none of the previous drive train options are available to the 06/07. Feels like GM did a lot of changes a little beyond a typical mid-gen refresh.
I know the tail lights for all 00-07 are interchangeable. I actually saw 00-05 Monte that had all it's exterior body panels swapped with a 06-07 (it can be done, owner told me it was almost direct bolt up, shy of a few minor issues). The big difference in the 06-07 trunk is starting in 05, GM got rid of the trunk lock. Out side of that, I am 90% certain the trunk lids are interchangeable.

Now the spoiler, there will be a series of nuts on the inside of the trunk lid to remove (depending on the car, you may need to remove some rubber covers). After that, yes, GM tends to use a strong adhesive to hold the spoiler to the lid. It can be a bear trying to get through/lift the spoiler off.