Imagine if someone had outside counsel guidelines from a dozen Fortune 500 companies during the 1970s, from the same companies or comparables during the 1980s, and likewise for the next two decades. Such a collection would allow a historiography of guidelines: a study of how the guidelines changed over time.
I suspect each decade would produce guidelines that are longer. Longer because more ideas are in them, more examples, more requirements, appendices, all serving to increase the sheer number of words.
The formats would change. For example, as the concept of rules laid down by buyers of legal services became accepted and understood, the introductory statements would shrink. As detail and exceptions encroach, indentation and numbering would elaborate. A diagram or graphic might show up in the later years and URL links in the most recent.
Third, the historiographer could quantify a pace of change. It would be possible to note the new ideas and the disappearance of old ones and chart the frequency of changes. Only in the 1990s would one find electronic submission of invoices; only in the last decade secondments. After the 1970s, no one mentions postage, perhaps. This analysis might show that companies revised their guidelines more frequently as time passed.
Assertiveness would change over time. The tone of law departments as humble supplicants might give way to assertive dominance: “Do not send more than one associate to depositions.” “Do not bill us for online research charges.” Broad statements of principle would yield to hard rules. No more “Bear in mind our resources are limited.” More “We will not pay for over-runs on approved matter budgets.”
Finally, careful reading of outside guidelines from major corporations would detect shifts in expectations of how law firms should respond to guidelines. Perhaps nothing was said in the earliest decades, but more recent guidelines insist that the relationship partner sign the document and distribute it to each timekeeper.