For the application of the second sentence of 1° of Article L. 5424-27, the average monthly amount of income from the self-employed activity mentioned in 1° of Article R. 5424-70 is determined:
1° By dividing by twenty-four the income corresponding to this activity mentioned in the two tax returns submitted for the assessment of the income condition provided for in Article R. 5424-71;
2° Where the tax returns referred to in 1° do not provide proof of twenty-four months’ income from self-employed activity, the self-employed person certifies on his or her honour the income from self-employed activity received for the missing months as it must be declared to the tax authorities for the calculation of income tax.