This address header should be used on GQ-4X only. It is used for extending the older willem adapter's compatibility on GQ-4X programmer.
The GQ-4X has integrated all address lines (A19,A20,A21,A22,A23) on a 40 pin ZIF socket. This adapter is designed for some old 32 pin ZIF socket style willem adapters are used on the GQ-4X. Such as TSOP48 adapter, PSOP44 adapter, 16 bit EPROM adapter. etc. Those old version adapters need to use extended addres line A19,A20,A21.
For all newer version (V2.0 and later) adapters, do not need this address header.