Are there any IAP models that do not support mesh on OS version 4.2.x?
Latest Instant OS version as of now is 4.2 which enables mesh support for 802.1ac AP's like 225/224's.
All the IAP models will support mesh except the below in Instant OS 4.2.x:
RAP3 - since it is a single radio AP
IAP-92/93 - these devices will not support Instant OS 4.2.x