Premiere Pro ExtendScript addSequence preset resolution inconsistency

When a developer calls app.project.items.addSequence(name, width, height, pixelAspect, duration, preset) with a preset name that exists both as a factory preset and as a user‑defined preset, it is unclear which preset’s settings are applied.

The ExtendScript documentation does not specify the fallback logic when the supplied preset cannot be uniquely resolved, and observed results vary between installations.

What precedence does Premiere Pro give to factory versus custom presets with identical names?
If the preset name does not match any entry, does the API fall back to default sequence settings or throw an error?
How does the presence of a custom preset affect the behavior when a matching factory preset is also present?