oK been outta the "J" loop for quite some time but one of my friends recently met up with a stop sign and truck thanks to the snow. Is a 2000 trunk lid compatible with a 99? I would think so since the new 04s and 05's are right? 
 
 
all the lids are interchangeable. the 2 different styles though are 95-02 and 03-05
 
 
Yeah 88-94 are all the same, and 95-02 are all the same, but 03-05 have the light bar across the panel...
 
 
the 95-05 cavalier trunk lids are essentially the same, but due to the red plastic piece on the 03-05, there are holes in the trunk lid.  that's the only major difference in the lid itself.