Staff labels and abbreviation after the first system

Every stave/instrument gets its full name at the start of the FIRST system. On every subsequent system, the label switches to a short abbreviated form (or is omitted for all but a few reference instruments in dense orchestral scores) — driven purely by space economy, never by ambiguity.

A multi-system score (barsPerSystem set, 2+ systems) that repeats the FULL name on every system, or omits it from the first.

Gould (Behind Bars, labelling conventions); Ross (The Art of Music Engraving, standard abbreviation tables: 'Vln.', 'Vla.', 'Vc.', 'S.', 'A.', 'T.', 'B.').

This rule is about where marks land on the page, so it can only be judged after engraving. Collision and spacing faults live here.