Revision 6 is the early adopter revision. It does not have the MCP73871 Li-Ion/LiPo charger or battery connector components mounted, and can only be powered through USB.
J201 and J202 (mikroBUS socket), and R204 (0-ohm resistor to apply 5V to mikroBUS socket) are not populated on this revision.
The Wi-Fi module WINC1510 order code used on revision 6 is ATWINC1510-MR210PB1952 (firmware 19.5.2). The firmware was upgraded to version 19.6.1 in production.
PCB revision 3.