When the Document ID service is activated it automatically generates a unique ID for each item in a site collection that inherits from the Document content type. At one time the middle portion of the ID was the integer ID of the list where the document was originally created. This was usually a small, one or two-digit number. Somewhere along the way this number ballooned and now, at least on one of my site collections, the number is about 8 digits long. I know I don't have 1 million lists in my site collection so what's up? Is this some sort of hack or some portion of the GUID? If so, I can't make the correlation.
Would certainly be nice to keep the Document IDs of tomorrow looking similar to those of yesterday....