"6.4.4.8" is the version of controller code it should loosely have parity with
"4.2.4.3" is the instant version.
"56707" is the build number which is just an incremental number internally. Its main purpose is to differentiate between two different builds of the same version of code (rare in the real world).
As of 6.5.2.0 both ArubaOS and Instant will have the same version numbers and the <AOS version>_<Instant version>_<build number> naming goes away.