There is an interesting gotcha with the licensing model in IDM. The activations are stored in an attribute DirXML-ACT3. Driver shims, when they handshake with the engine, include version strings for both ends.
While this is unsupported, I often try the latest shim on an older IDM version, just to see if a particular bug is fixed in the new shim. What I have noticed is that the activation for the engine is one thing, and is based on the engine version - which is obvious.
The activation for the driver is based on the shim's version string. Thus, if you have the AD driver for, say, 3.01 running and activated, then you update the ADdriver.dll to the one from the 3.5 distribution, (this is for testing only, of course - no one would ever do this in production), you will see the activation go away! You are then back to the 90-day license.
What you can do, if this bothers you, is to add the activation credential for your IDM 3.5 license. This will add a value to the DirXML-ACT3 attribute. When you use iManager's Activation info, you will see that you have multiple activation licenses, which is perfectly fine and normal.