Differences for:
- JW811A Aruba Instant IAP-315 (RW) 802.11n/ac Dual 2x2:2/4x4:4 MU-MIMO Radio Integrated Antenna AP
- JW813A Aruba Instant IAP-315 (US) 802.11n/ac Dual 2x2:2/4x4:4 MU-MIMO Radio Integrated Antenna AP
- JW810A Aruba Instant IAP-315 (JP) 802.11n/ac Dual 2x2:2/4x4:4 MU-MIMO Radio Integrated Antenna AP
can be found on Domain Regulations they adhere...those three Instant AP's SKUs, respectively, support and must be used into three very distinct geographical zones: RW (Rest of the World), US (United States of America) and JP (Japan).
WRT your question, this basically means that an Instant AP with US SKU can (or should) only be used in the United States and - for sure - it can not be a part of a Cluster made by other RW IAPs and vice-versa, an Instant AP with RW SKU can (or should) only be used in the Rest of the World (so United States and Japan excluded) and - for sure - it can not be a part of a Cluster made by other US or JP IAPs.
That's because each SKU (US, RW and JP) is enabled to work in a specific Regulatory Domain (respectively US, RW and JP).