If you can’t prove it- don’t say it… but when opinion is called for, base it on facts and outline them as the basis for your judgement.
Keep in mind that all external documents should be considered to be read by outside parties including hostile legal counsel, and competitors. And archived and retrievable- anywhere, anytime, worldwide- thanks to Google.

Confidential privacy advice courtesy of Google.
Confidential privacy advice courtesy of Google.

Here’s an  ironic example : note  the  “confidential sponsors only” status on the bottom of this slide from a presentation posted on the world wide web. Note the last bullet point: Issues Management: Privacy as a key topic. Physician, heal thyself!
My 3 guidelines are to make certain that your writing is therefore:

  1. Strictly focused. Stick to the topic of concern. No “subject creep.”
  2. Veracity incarnate. If any aspect is uncertain, give the reader guidelines so that they may make appropriate inferences.
  3. Necessary. The people who will be receiving your work are busy too. Is it absolutely necessary that they get your document? Ask “Why?” 5 times. Remember, like the slide above, it could end up on Google forever.

As Santayana once observed, “It is helpful for a system of philosophy to be substantially true.”
Truth may not be an adequate defense to certain readers, (it may in fact be hostile to their intentions). But as precision manufacturers,  we stand nowhere if not on the facts and data.