You can use 623B in otgs if the hit count is low. for example if you do combo > 2c 5c 623{b} 5b 2c 623B it wont work but 5b into 623B does.
For 4way off of 623C in the corner after 5b 2c 623c it creates a gap in the corner. When you dash at them and jump straight up your dash momentum carries you to the other side if you dont press a button. A simple 4way is:
jump over, late airbackdash jc
jump over, late airbackdash jc(wiff) 2a/2c (i'm not sure if 2a is a low, also spacing usually requires 2c)
jump over, jump and air backdash towards the corner and jc (the faster you do the IADB the harder it is to react to it)
jump over, jump and air backdash jc (wiff) 2a/2b/2c
you can also do these midscreen, i haven't figured out the timing for IADB jc yet but i've hit it before. I dont buffer 496 by the way, i do 7-6AB. It might be easier to hit by using 496
also i might be completely wrong about 623b in otg and might be confusing it with 623a