You're right. GSN did the G/T Top 25 on their 2nd Anniversary. It's been a while since I watched those tapes -- I just found one of those tapes in the box and I can confirm it was their 2nd Anniversary, which means it was even longer back that I had worked with that co-worker at the place-that-shall-remain-nameless. Carry on.
I believe GSN obtained the rights to TPIR not long after, so it would make sense that it wasn't in the marathon.
GSN came out at a good time between the OJ trial and taboid talk shows.