Well done with the photos that will be helpful.
Looking at the wires I see that White+orange trace wire (the other half of the orange pair) has been connected at some time in the past, I'd guess before the current NTE5a was fitted.
Also bearing in mind your previous comments about the noise you heard on the corded phone and that fact that you have a 2nd business line, it will be a good idea to discover as much as possible about all your wiring as soon as possible.
So a couple of things, as you've had some drops in sync, either from noise or just moving things to the test socket etc. it would be a good idea from now on to first, drop the PPP Internet session by clicking Disconnect in the modem/router Interface, wait a minute and then power down the modem/router, then wait another minute before unplugging from the line. Take at least 10 minutes doing whatever needs to be done before plugging in and powering up again, then click Connect at the modem/router interface. This procedure helps prevent the Exchange DLM from thinking you have a (worse) dropping connection.
Adopt the same procedure for your business line if/when there's a need to unplug it.
Also at this point I wouldn't consider a Filtered faceplate as it could mask any issues present (and will limit where you can plug in the modem/router).
Where are you currently plugged in? If you have moved back to the test socket, do you have the cordless or the corded phone plugged in?
Stay plugged into the test socket and take the stats. Swap the phone and take the stats again. If you are not at the test socket leave this until later.
Wherever you currently are, follow the Disconnect method outline above and stay unplugged.
Remove the NTE5a faceplate, then unscrew the rear plate off the wall box and take a picture of the wiring in the box as well as at the rear plate. Be careful not to pull the wires out of the rear plate.
Take pictures of the wiring at the back of both the extension sockets and in the mounting box next to the business line NTE. Do not disturb the business line for the time being.
If you weren't in the test socket initially, connect up now, and take the stats with each of the phones.
Can you confirm that all the
Microfilters you use look like this?
