Did they even offer the Suburbans as classics from 99-00 though? I've never seen one. Rock Auto doesn't have any parts listings for them, either. I think the '99 and '00 Suburbans were on the GMT800 platform only.
They still had the 400 style in 99 and 2K, they didn't offer the GMT800 Burbs/Tahoes/Yukons until 2001, everything I'd read on the 99-2000 GMT400s kind of led me to believe they were all considered classics.
Some Yukon Denalis/Yukon XLs were released from GMC in late 2000, but it was mainly OBS to that point.
But, like I say with all my informational posts, someone can step in and expand on this or correct me.