Full Tag Path in an expression

So I’m trying to work with intermittent communication with my plcs and to solve the problem I want to get the last good value if the current state is bad quality. I wrote a script that will get me either the current value if it’s good or the last historical if its not.

But here’s my problem. If I make an expression tag that is set to this value then I have to get the full tag path to the OPC tag that contains the value using expressions and I can’t figure out what the reference is for that.

I ended up working around this issue by writing a script on the valueChanged event that conditionally writes it’s value and timestamp to memory tags if the quality is good.
If the live value is returned as null I apply formatting to the display and point at the historical value.

As far as I was able to determine, there is no method to get the full tag path with expressions.