Unless and until otherwise provided by ordinance of the County Council within the limitations provided by public general law, the aggregate amounts of bonds and other evidences of indebtedness outstanding at any one time shall not exceed ten per centum upon the assessable basis of the County; provided, however, that (a) tax anticipation notes or other evidences of indebtedness having a maturity not in excess of twelve months, (b) bonds or other evidences of indebtedness issued or guaranteed by the County payable primarily or exclusively from taxes levied in or on, or other revenues of, special taxing areas or districts heretofore or hereafter established by law and (c) bonds or other evidences of indebtedness issued for self-liquidating and other projects payable primarily or exclusively from the proceeds of assessments or charges for special benefits or services shall not be subject to, or be included as bonds or evidences of indebtedness in computing or applying the per centum limitation above provided. All bonds or other evidences of indebtedness issued under the authority of The Sanitary Commission Act shall be construed as exempt, under clauses (b) and (c) above, from the per centum limitation in this section provided, but shall continue as heretofore to be subject to the per centum limitation as from time to time provided in said Act.