When you have an ACDF there is a 20% risk of needing surgery on the disc above and below the site of fusion due to accelerated degeneration from pressure put on the discs.
My surgeon told me in a 10-15 year time frame.
Like the above post says, if you are continuing to do strenuous and high risk neck activities then your risk is even higher of having continuing neck problems.
If I decipher your post correctly, you now have a problem with your disks at C-6 and 7. This is the same situation as occurred previously when you were required to have surgery at C-5 and 6. I suppose you could have another fusion at the lower level in the C-spine and that should take away the pain once again for the most part. Or could be you have a pinched nerve at that location for some reason, and usually medication and physical therapy will clear that up.
There's something about either your work, which you say is strenuous, or the way your anatomy is, that causes your cervical spine to goof up. So, if you go for surgery again, after you have rested a while, they should also put you in a little physical therapy program, so you can strengthen your neck muscles and also keep them flexible. I still do exercises for my thoracic spine to this day, and it was injured many years ago.
Also, if you would rather put off surgery, there are medications that help spine pain, along with physical therapy, that might help for a while. You could also get some sleep medicines, perhaps. In the meantime, get you a solid foam pillow (not the chopped-up kind) to support your neck better, or consider sleeping in a more upright position, like even in lounge chair where it pushes back. Applying heat to the neck sometimes helps with pain, too. And an ordinary alka seltzer is easy on the stomach and yet provides anti-inflammatory relief and helps with sleep.
But obviously you need to sit down with the neuro or whomever ordered the most recent scan and ask him what does he suggest you do for your neck problems. And you may wind up having to retrain for different work, so as not to put too much strain on your neck.