Although I have not read DEC's (Digital Equipment Corporation) documentation, but I've come across a 1990 book that mentions DEC's approach to documentation:
> Digital Equipment Corporation noted in their 1983 internal documentation guidelines that user documentation should be written first — not last as is traditionally done — because the user documentation is an excellent way to debug the design of a system or a program. “If a writer finds it difficult to document a system, the problem is probably the system not the writer. Holes in design, obscure constructions, and apparent contradictions become starkly visible in the documentation.”
(From book: Writing better computer user documentation, 1990)
> Digital Equipment Corporation noted in their 1983 internal documentation guidelines that user documentation should be written first — not last as is traditionally done — because the user documentation is an excellent way to debug the design of a system or a program. “If a writer finds it difficult to document a system, the problem is probably the system not the writer. Holes in design, obscure constructions, and apparent contradictions become starkly visible in the documentation.”
(From book: Writing better computer user documentation, 1990)