A system may prove cost effective in automated conversion for one clump of documents but fail utterly on another clump. This coarse deficiency is not a property of a swing from one type of document to another but appears to be a property of a much more subtle, and less controllable, shifting of the context in which the document clumps originate. One executive's office has a different optical character recognition requirement from another and his needs change, one month he wants newspaper articles read and another he wants sales books read. Accepted drawing practices are different year to year, manufacturing site to manufacturing site, design firm to design firm. This is not the exception but the rule.
People always seek to minimize the content on paper without sacrificing the communication.
This means that, inevitably and with few exceptions, a clump occurs because there is a natural clumping of common knowledge among people in practice. We know of many instances, for example, where printed wiring tooling is assumed, by the workers in the printed wiring board shop, to have defects that they will manually fix during manufacture. The tooling is not, actually, authorative. Of course, the situation is even worse in the case of mechanical drawings that do not represent the tooling itself. Other systems exist for customizing pattern recognition by knowledgeable code writers.