how export groups are working?

[SiriVFX]

i try to export particles in different groups, to apply different material after that.
but if i use global export(export node in a single event) it seems to export every visible particle.
thought i turn on export group A in display node and export node it would only export all A marked particles.
but the particle disappear when i select a a group in the display node.

if i put the node in an event it exports only the particle in that event.

and i also dont know what this overlapping/equal/not equal does.