This from Simon Eadon, formerly of Decca:

There were no strict mic set-up guidelines as such- we all ploughed the same well-worn furrow that had previously been ploughed, I suppose. B&Ks were always regarded as a bit bland at Decca so we never used them. Jimmy Lock (who succeeded Kenneth Wilkinson as head of the department) was in favour of us (then) younger engineers experimenting with mic set-ups. Wilkie, on the other hand, would condemn a recording that was not done accoring to previous (more often "his") custom and practice regardless of whether it was any good or not! As a matter of interest, the Beethoven Symphonies which I engineered for Arte Nova with the Zürich Tonhalle Orchestra conducted by David Zinman were started with M50s. When we were made redundant by Decca I continued the series but no longer had access to these mics - hence the Schoeps 2S with balls. The CD with Beethoven 5 was done with 50s all the other CDs were done with Schoeps. No one seems to have spotted the difference. I still keep meticulous set-up details which we did at Decca: mic types, heights, preset gains, pans &c. These session records went back to the 1950s. Now with digital cameras one can have an amazing pictorial record of recording set-ups too - really useful when you go back to a venue: if you like what you did last time you know what to do again - and if you did not - you can start altering the set-up. Happy recordings!