TBD means "To Be Decided".
In the case of ArubaOS 6.4.3, the guide describes AP-93.
In the IAPs with version 6.4.2.6-4.1, the release note said: "Support for IAP-92/93 is reintroduced in Instant 6.4.0.3-4.1.0.1 and will continue in future 6.4.x.x-4.1.x.x releases."
There are some limitations described in both guides.