Timeline Zero

Timeline Zero is the "Greenwich Meridian" of the Earth-centered time trunk. It is the highest-probability Earth-centered trunk and as such has no sub- or supra-lines (since all of its sub- or supra-lines would be numbered timelines in their own right, with the sub-lines likely to the left and the supra-lines likely to the right). The Earth-centered time trunk is known to the Great Simulation by its shorthand alphanumerical designation HNK12864-9, which in turn is said to be a transliteration of the last few glyphs of the full timeline designation. (The Lion of God, p.262)

Does Timeline Zero have sub and supra lines?

Short answer: No.

Longer answer: Please note that any previous allusion I may have made in Timelines stories published prior to The Lion and the Darkness, The Tale of the Crane Princess, and A Huntress on the Rocks that Timeline Zero does in fact have sub- and supra-lines has been abandoned; you can treat it like the reference in H. Beam Piper's "Police Operation," where Verkan Vall is tested to ensure he is "their" Verkan Vall when he returns from killing the Venusian Nighthound in what is apparently "our" Paratime timeline. John Carr suspects this was never mentioned again because having infinite Home Time-Lines would have created a paradox in which there would have been infinite timelines where the transpositional time "secret" was known. Later stories made it clear there was only one Home Time-Line where the transpositional time secret was known, and the Paratime Police's "Job One" was to keep that secret safe.