I haven't been able to get credit for a 6th map yet.
I can't seem to find a solid source on which maps to look out for.
TA and XBA both say there are 6 maps,
But halo wiki says there are 8 possibilities
- Attack on Sanctum
- Escape From A.R.C.
- March on Stormbreak
- Raid on Apex 7
- Skirmish at Darkstar