I am having a one of those moments. Why doesnt the PartMtl table contain the revision number of the material in a parent? There is the revision of the parent part.
I think this goes back to the revision vs. part discussion. The APICS person will tell you that if the two revisions are not interchangeable then each should have their own part number. That way you can call out the one you really need.
Imagine the programming complexity too. Every time you checked in a new revision, how would Epicor know which components to update and which not?
Hmmmm I sort of agree. Two fields are just being used as a unique identifier i could just as well use part references such as PART1-1, PART1-2 in a single field
But we do have part revisions and they are used within Epicor, but just not consistently.
So when I open method tracker and look at an assembly how does Epicor determine which parts (revisions) make it up.?
Effective date, usually today.
Two revisions of a part could have effective dates in the past making both ‘effective’
So Epicor would choose the most recent?
The “most recent” 
In other words, the one that falls between the active effective dates. So if you had a newer one not yet effect, I THINK it shows the current one until the next one comes into effect.