Using Rules to Concat a Form Tracking Number

Hi Experts,

I'm attempting to use rules and filters to set the value of @TrackingNumber to create a unique value for my filename when submitting to SharePoint.

FYSA: I have a SharePoint List with OpLocationCode, OpRegion, OpBranch, OpUnit, and OpRegionCode all in a single SP List.

When a user makes a selection on the @OpLocationCode control all subsequent fields populate using rules and filters. For Example, when a change is made to @OpLocationCode the following rule/filter runs on @OpRegionCode @OpRegionCode[OpLocationCode = @OpLocationCode]

I have 4 of these rules/filters set up to cascade the correct values automatically into the controls that are dependent on @OpLocationCode.

At the end of these 4 rules/filters I have a 5th rule that attempts to Set the value of @TrackingNumber to:
concat(substring(now(), 1, 5), OpRegionCode, "-", OpLocationCode, "-", substring(now(), 6, 2), substring(now(), 9, 2), substring(now(), 15, 2), substring(now(), 18, 2))

The end result should make the tracking number look something like this:
2015-SER-HMU-02252956

Instead the tracking number looks like this:
2015--HMU-02252956

Basically, the "SER" which is @OpRegionCode is missing. Now I believe that is because the value for @OpRegionCode is blank at the time the 5th rule runs to set the tracking number. (I've tested by setting a condition that says run if @OpRegionCode is not blank and the rule does not run)

I realize that I could just have the tracking number set on form submit; however, I'd really just like to have it populate a tracking number when a user is done selecting an @OpLocationCode. Can I accomplish this?