You have things a bit mixed up, I think.
The track number has zero to do with the playlist. That is the track number is the [Track #] field from the file. This is the track number from the album the track comes from, the order it appears on the CD.
The Seq is the separate order maintained for the playlist. That is the "hardwired" order of the track on the playlist.
If you added 10 tracks from your 10 favorite albums, each track being the first track on the album, when you looked at the playlist, all of them would show [Track #] = 1. But they would each have a different Seq.
Of course this being JRiver, you can sort your playlist any way you want by clicking on the column headers, and then the playlist will play in that sorted order. You could sort by track, or by name, or whatever, just as anywhere else in MC. Sorting will never change the [Track #] field. Only the Seq field has special meaning when a track is added to a playlist.
You can look at the wiki page for playlists where this is explained.
If you want to permanently update the seq (short for sequence, the playlist order) based on your sorting, click the Update Order button in the top pane.
Make sense?