Notwithstanding any other provision of this Constitution, Mobile county shall continue to have and possess all of the rights, powers and authority granted to it by amendment XVIII [18] of this Constitution and Act Number 246 of the Local Acts of 1927 [p. 151], as the same has been heretofore amended, and shall have and possess the power and authority to become indebted for the construction or erection of public buildings, bridges and roads within the limit prescribed by section 224 of this Constitution; provided, however, that all debts incurred or bonds issued by Mobile county under the provisions of amendment XXIX [29] shall be in addition to the limit fixed by said section 224, and shall not be taken into account or considered in determining or arriving at the debt limit of Mobile county under said section 224, and provided further that the six and one-half percent (6 1/2 %) limitation in amendment XVIII [18] aforesaid shall be construed to refer not to the total amount of bonds issued under authority of the amendment, but to the total amount of bonds so issued which may be outstanding at any one time.