The IRM is public, enormous and organized better than most people think. Learn the numbering, the dates and the redactions, and you can read the same instructions the IRS employee on your case is reading.
The IRS can change an employee's instructions overnight through an interim guidance memorandum or an IRM Procedural Update. If you only read the manual, you may be reading last year's rules.
Every call, deadline, excuse and decision on your case is typed into the Integrated Collection System. That history follows your account to the next officer, the manager and Appeals.
The IRS employee on the phone is looking at a screen fed by several systems with their own rules, update cycles and access limits. Knowing which is which explains a lot of IRS behavior.
The IRS keeps a file on your collection case: histories, notes, financial analysis and correspondence. You have a right to most of it. Here is how to ask, and what will come back redacted.
A threat, a show of force or a history of violence toward IRS employees can put a PDT flag on your account. It shows up on IRS screens for years and changes how every contact happens.