They released Carpet Crawlers '99 on the Turn It On Again: the Hits compilation. I remember I went and got it when it was first released during the year I graduated high school. I don't recall if it was early or late 1999, but I remember it was very cold out when I walked to the store to get it (I was in Wisconsin at that time). By then the 1970-1975 Archive boxset had already come out, as I got that for Christmas in 1998.
As for when CC99 was actually recorded, all I remember reading at the time is that it was put together remotely with each band member doing their own contributions separately and then emailing it to another-and it was a couple years in the making, before the hits collection was released. I don't know anything further regarding what their original intentions were for the song - but there was nothing that said it was already worked on as early as 1995...