Confusion about bpy.data.version in Python

I’ve been trying to download the correct versions of blender that correspond with my older files’ most recent saves. I have been using bpy.data.version to determine the last saved version of my .blends. I have noticed the following:

As a test, I created and saved a file in version 4.0.0 (as per the bottom right corner and bpy.app.version). Upon reopening, however, bpy.data.version shows the file as “4.0.36” even though it was made and saved in version 4.0.0.

I have also noticed this with files saved in version 3.6, where bpy.data.version will show “3.6.13” regardless of if I save from Blender 3.6.5 or 3.6.10 (again, as per the bottom corner and bpy.app.version).

What is causing this discrepancy? What does the 3rd number, such as the “36” in the first example, represent in this situation?