1. scope x24
The oldest (oldest topic dating to 2013), and is a clear tag; its usage guidance:
[...] which questions are on-topic here.
2. on-topic x16
No usage guidance; same as scope?
3. off-topic x29
For questioning closures or closing questions? Its usage guidance:
[...] what subjects are considered off-topic for the site
Maybe they're on-topic, so isn't that the same as scope?
Deciding whether something is on- or off-topic fits neatly under scope. The other two just add confusion and make it harder to browse the topic. Should they be merged under scope or have I missed something?