so we talked a bit about it and there is unfortunately no way to do this ...
Thanks for having taken the time to further investigate and discuss.
... depending on what you are trying to do, a general shift of design might be necessary when you run into major problems.
I wouldn't mind a shift of design, unfortunately at this point in time I am out of ideas how to proceed.
Maybe I am too focused on trying to reach my goal using the available cache. If there would be any other possibility to obtain the information I need to use ... I am all ears.
The goal I am trying to reach might have been lost with all the technical details, so let me recap it with an example here:
Let's say I have a regular polygon cube with 6 faces, 8 points.
I put this cube into a subdivision-surface, resulting in the cube being smoothed, modifying the points' coordinates.
What I would like to achieve is to know the modified coordinates of the 8 points.
So, traversing the cache of the SDS and getting the particular cached object is one thing ...
But since the SDS will subdivide the input object, the resulting cube (in the cache) will have more than 6 faces, 8 points.
Second step is then to find out which original point index matches which point index in the modified object.
Cinema4D does seem to have a way to know that relation.
With the example of the cube under an SDS, enable islone editing, switch to point mode and select any of the 8 points of the cube.
Cinema4D will display to original point as selected, but also the modified point.
The one point has the original coordinates, the other has the modified coordinates.
My goal is thus to find a similar way to obtain the modified coordinates of a point.