So, theres a few things to do with this.
If there is no upgrade in the works, the best way to lay out a safety system short of running everything back to IO (which we literally just did), is to have specific terminal blocks laid out in a cabinet making it easy to check where the safety chain is broken.
The safety circuit gets laid out in a long series so if anything is broken it can stop the system just the same. The idea is, every single device has both its wires run back to the main cabinet, as opposed to running from one device to another. even if the two devices are right next to each other you run those wires back to the main cabinet.
When you run those back to the main cabinet, it would look like this
Main power -||- out to Device 1
In from Device 1 -||- out to Device 2
In from Device 2 -||- out to Device 3
In from Device 3 -||- MCR
When you lay it out like this, all it takes is running a meter down a terminal strip and where the power is broken, you know which device is not functioning.
The New way to do it is to install safety devices that have a NC and a NO contact inside, the NC contact stays for the E-stop, but the NO is now used for a PLC input to show which device is going to be open/bad. I'll be going out to a site to download an updated program for this exact type of safety layout in a week or so. and my updated Panelview program will have a page dedicated to showing door and safety status so anyone can click on it and see what is open and what isn't.
The newest way I've seen is to use ASi network safety devices.... they are individually addressed devices on a two wire node network that can activate a safety relay and also give feedback at the same time with minimal wiring. Unfortunately these are harder for regular Joe to integrate and more expensive upfront, but they look solid (never used them).
https://new.abb.com/low-voltage/products/safety-products/as-i-safety