I believe that MAC-V-SOG knives were contract-manufactured in Japan.
If you have a real one, it should be valuable but you will need to prove the provenance of that knife. If you can tie it to a known Operator and have signed letters and photos, it will greatly increase the value.
Because these knives were 'sterile', it is very hard to prove. There are more fakes than authentic ones around.
Can you post a picture of the knife with sheath?