Whether an encoder is absolute or relative is a physical characteristic of the encoder. It does not matter how the encoder is installed or used. For example, the add-on encoders that Astro-Physics uses are Renishaw absolute encoders. They have what are effectively microscopic codes on the encoder ring that provide 62 million unique addresses around the ring. The read head can determine its position over the encoder ring without have to count ticks. They do not get lost no matter what you do, including power cycling. You do not need to re-zero them. Ever.*
The encoders are installed on AP1100 and AP1600 mounts by attaching to the worm wheel. As long as the clutches remain locked, the mount cannot get lost. If you release the clutches and move the axes, the worm wheel does not turn, so the encoders don't "see" that movement. The new Mach2 installs the encoders on the axes themselves and will "see" movement, regardless of whether the clutches are locked or released. The Mach2 cannot get lost no matter what you do, including releasing the clutches.
The Renishaw encoders are well documented by Renishaw, so there is no need for speculation (I have tried to summarize what's already been thoroughly discussed regarding their use with an Astro-Physics mount). The encoders used in iOptron EC and EC2 mounts are relative encoders and have different characteristics. I am not aware of the manufacturer and don't remember the specs (although some of the specs have been discussed on Cloudy Nights). The encoders used on the 10Micron mounts are proprietary to 10Micron, and I'm not sure how much technical information that they provide.
I am not familiar with the machining world or language at all. I only know what I know about the encoders used on the Astro-Physics mounts because this stuff has been hashed out a number of times, both here on Cloudy Nights, and also on the Astro-Physics user group, complete with references to the Renishaw data sheets. I also know the behavior of the Renishaw absolute encoders on an Astro-Physics mount because I own an absolute encoder-equipped AP1600.
I'm sorry that this has gone way, way beyond the point that OP raised at the start of the thread, but there are lots of statements above that are just plain wrong - specifically in the context of high resolution encoders used on astronomical mounts.
* Note that Astro-Physics does have a utility that is used to "home" the encoders. This is not because the encoders require it. It is because of how the encoders don't "see" movement of the axes with the clutches released. The purpose is to establish the position of the axes relative to the worm wheel (the worm wheel is tracked by the encoder). This utility does not apply to the Mach2 because the encoders are directly attached to the axes, as above.