I have an older 1989 Pearl BLX kit. I ordered and recieved it new as a 'kit', but the badges are not sequential, tho they are not too far out number-wise. I didnt know Pearl even date-marked their shells, but i think generally speaking when a kit is shipped out from the factory the shells are more or less of the same vintage/ month of the year. I couldnt pick any difference with my shells as far as different sound, ie it all sounds like the shells belong together as a kit. If the serial mumbers are matched/sequenced, i cant see any problem. Face it, drums are usually mass produced these days, not individually matched to create a set (unless you are a big name endorsed player) so basically a maple kit will sound like maple, birch will sound like birch, regardless if each drum was manufactured days/weeks apart. If you are concerned about the year the kit(as a whole) was made, personally i like to see shop reciepts of sale etc if buying 2nd hand. People that keep reciepts are usually a bit more caring/proud of their equipment than those who dont. (im just fussy that way.)