Without knowledge of what "Level 4" is referencing in your docs, I can explain how I've done document control numbers in the past:
For all forms, things that get filled out by staff, they followed a dept-form#-version# number format. Example: QAC-101-1.2. The version number decimal would be changed to reflect minor changes on the form (adding an extra signature line, an extra check box, etc). The primary number would reflect a large scale revision (totally rewriting a receiving form would bring about version 2.0). I never added revision histories to forms to keep them from being too long on the floor, but I do keep the revision histories in a change control log where all document changes are recorded.
For SOPs, programs, policies, they'd follow a xx.xx.xx.xx number format similar to the SQF structure. Example: 2.5.7.1. I never mirrored their format, instead normally splitting my FSQMS into 29 chapters. First number denotes the chapter, second number counts the documents within that chapter, third and fourth numbers denote sub-programs related to the documents in that chapter. So 14.2.0.0 might be my Equipment Sanitation Program within my Sanitation chapter, where 14.2.1.0 thru 14.2.12.0 might cover 12 different sanitation procedures for specific equipment. Those numbers never change when a revision is made to the document, as the document control number does not include a revision number. But the full revision history of those SOPs and programs is at the end of each one, and the current date of that doc is joined with a supersedes date that correlates to the revision history.
TL;DR to the OP's question: I don't use revision numbers in my SOPs/programs, but I absolutely do update the date when ANY change is made, and cover it in the revision history within that document.