While not completely analogous, I have done the same thing with Master Cleaning Schedules when taking over a Sanitation department.
I look at the current periodicity and question items that I think (through previous experience) are either done too often or not often enough.
I let the scheduled cleaning take place and then when the next scheduled cleaning comes due, I go out and do a detailed inspection of the equipment/area prior to the cleaning activity.
I then make a determination whether the SSOP frequency needs to be adjusted. I train my sanitation supervisors/leads to always inspect an area before having someone clean it. If it does not need to be cleaned, don't spend the time cleaning it and document that the area was inspected and did not need to be cleaned.
Obviously, this only works for some items that have a fairly decent interval between cleaning. For example, when I started my current position, the CCTV cameras were scheduled to be cleaned every two weeks. I inspected a representative sample of cameras throughout the facility at the two week mark. Did not need to be cleaned. I looked two weeks later. Did not need to be cleaned. I looked two weeks later. Some of the cameras in the mixing areas had a light buildup of flour dust.
So, I broke those particular cameras out into a new line item and changed the cleaning frequency to every 45 days. The rest of the cameras I changed to 45 days and changed the description of the SSOP to "Inspect and clean if necessary".
I've never had an auditor ask to see an equipment manual to determine cleaning (or PM) frequencies.
To echo Glenn though, If I were an auditor and observed a piece of equipment that obviously had not been PM'd, I would certainly ask to see your PM schedule for that equipment and determine when the last time it was "supposedly" PM'd. If your records say it was done last week, I'd probably question you on the validity of your PM records and I "might" ask to see what the manufacturers recommendation for PM is.