WhoData - you're talking about EXPANSION modules.
A 206E is used strictly as an expansion module.
A 206 without the "E" is actually a "Baby Partner" system, a 2x6 key system that can be paired with a 205E to make a 4x12
OR it can be placed in a 5-slot carrier along with a processor (Partner Plus, Partner II, or Partner ACS) and even though it is a Baby Partner system, it becomes an expansion card instead. All of its features and functions come from the Processor in this situation.
The only feature I recall through the revisions of 206 expansion modules was the ability to light MW lights on single line phones. That, and the earlier releases would shut down a station port if the data pair became shorted, requiring a power cycle to restore, while the later ones were more robust.
Finally, for ANY Partner system, you can dial Feature #1 while off hook on an outside line. You will hear a series of touch tone "1's". Note the number and pattern of the beeps, and there is a cross reference on Avaya's site to determine the version and release of the Processor.