What does t6-7 4mm post disc protrusion with superior extrusion extending behind the lower on half of t6, measuring 9mm cc, causing mild impression upon the cord at and the midline mean & serious?

Potentially Yes: If this progresses it may produce pressure on the spinal cord leading to neurological damage and changes due to that. You should be seen by a back specialist and have this discussed in detail.

MRI findings without: Clinical symptoms or exam findings in this case mean nothing. As we age, degenerative changes occur normally with discs that can bulge or even herniate without causing symptoms & even when they do, most are treated without surgery. The most important findings are on the physical exam and history in terms of any neurologic findings. On repeat MRI 6 months later, 60% of hnps are gone or smaller.

May be serious: Any symptoms? 80% of the population have an asymptomatic disc bulge. However, disc extrusion is more serious and depending on the degree of canal stenosis and clinical symptoms displayed, surgery might be the right choice for the long run. Image: your disc extrusion sounds like it is more centrally located compared to the image here. Would certainly see a surgeon regarding your condition.

Pushing on Things: If these herniated disks are causing pain then getting epidural injections may be helpful. However if you are doing OK and no pain, then I would leave them alone. Eventually they will heal as much as they can, but can take as much as 6-9 months to resolve. Unless you are getting increased pain or weakness, I wouldn't worry.