Yes, there can be low compression in at least one cylinder and the car could still start ok, so long as the glow plugs are working well.
Had that happen with the first engine I had in my 81SD. Engine would start just fine and run ok, except for a smoke cloud.
Best to run a compression test and get the facts. New these engines will show 425 lbs compression. They will continue to run until the compression drops below the 225 range, but probably will not run well.
I have been told just let em run until they get to where they won't start any longer. Not sure about that, but it can be done.