They can side tech the 4K stun, so JO 66B misses, so I'd never use 4K.
And I say JO/GL, but I've seen JS/GS. All depends on your preference.
Is that what causes the 4K to miss? When I do the JS 66B, 66B BE, GS BT B+K, 4K, 666B after the GS BT B+K there will be one of two things that happens. Either it get sucked in head towards, or get bounced away feet towards. Either way an immediate 66B will hit them, but if you try to throw out the 4K afterwards only the one where they were sucked in head towards will be hit, while you will whiff the 4K on the one with the feet towards knock away. Im getting better at visually confirming which one I get so I can sneak in extra damage if possible, but never figured out exactly what caused each situation.