If you were a resident of South Carolina when you entered the military, you remain an SC resident for tax purposes even when you are stationed outside South Carolina due to military orders. South Carolina is your State of Legal Residence (SLR).
If you wanted to change your SLR, you'd have to fill out a form DD-2058 and submit it through your pay office or admin office for processing. Changes to your state of legal residence may not be made retroactively.
As an SC resident, you are required to file an SC tax return every year. But your active duty military pay is not taxable by any other state.
Therefore, it sounds like you have to file an SC return for each of the years you missed. And an amended return for each year in each state in which you filed by mistake.
This is a big chore and I personally think you'd be better off seeking the services of a professional tax preparer or accountant, rather than doing it all by yourself.
Finally, be aware that it's only your active duty military pay that is exempt from income tax in other states. Any non-military income you had in another state would be taxable by that state.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
