If you are just starting out to set this up then you may not have made any final decision about how you name the files yet. If you already have all your files named as such then the answer is different.
What the variant rule does is look for a delimiter to separate the core file name from the revision.
In your case you could use the underscore "_" and code to use that as a delimiter. However you have two of those separated by the would "Rev". So if you're just setting up you naming standard I would dump the word "Rev" and just call it "4010-13_A.prt". This will save on typing and eliminate differences between "Rev", "REV" and "rev" which aren't necessarily the same thing in file naming syntax.
I would be so keen to get rid of that Rev that I'd clone the assemblies in necessary to remove it.
If however you're forced to stick with it then use the whole thing as your delimiter coding for "_REV_" should separate the core file name "4010-13" from the revision letter "A" or "B".
Lastly again if you're starting out then why not use the Military versioning method, "4010-13.1.prt" works as does "4010-13.1.1.1.prt" you can concoct as system whereby you have full releases, milestone releases, and versions that users increment rather than allowing them to overwrite each others work. It is the best and most flexible option. You don't have to have a high level of complexity but you can choose to use it if you need to.
When you get it to work set up your directories simply and not too deeply nested. If you search a deeply branching directory structure you find that an earlier version in a higher directory often gets preference over a later one buried further down the directory tree. This is just a limitation of how versioning rules work that depends on you controlling your work flow sensibly. We have worked with it for some time with few problems in this regard because we understand and work with the system.
Cheers
Hudson