Here's a simple tool to help you tell how incomplete ISA100.11a actually is...

Here is a simple test to determine the "completeness" of ISA100.11a.
Search for the words, "not specified" in the ISA100.11a document.  The words appear 57 times.  Is some cases the reference is for another spec, meaning look there not here.  However in many cases, the feature is not specified.  Here’s an example from the specification – 2 Figure 25 – Centralized system management

3 The distributed system management architecture is shown in Figure 26. Note that distributed

4 system management is allowed in ISA100.11a:2008, but is not specified. ISA100.11a:20085 provides an informative and general description of distributed system manager operations.6 This implies, in practice, that devices delivering distributed system management functions7 may be cooperating in a non-standard way. It is anticipated that more aspects of distributed8 operation may be specified in future releases of ISA100.11a.
Contrast this to the WirelessHART specification, in which everything is clearly specified, even the optional features...the vendor who is trying to build to WirelessHART is told exactly how to do it, and exactly what will pass compliance testing ahead of time.
This is another problem I have with the standard, and why I said it was half baked. We've all done an enormous amount of work on this standard, and it has the potential to be very very good-- so why blow it now?
Just so we can announce at ISA that we "have a standard"? Are we going to find a chimney and make white smoke too?