Aggregation of periods

1.   For the purposes of applying Article 6 of the basic Regulation, the competent institution shall contact the institutions of the Member States to whose legislation the person concerned has also been subject in order to determine all the periods completed under their legislation.
2.   The respective periods of insurance, employment, self-employment or residence completed under the legislation of a Member State shall be added to those completed under the legislation of any other Member State, insofar as necessary for the purposes of applying Article 6 of the basic Regulation, provided that these periods do not overlap.
3.   Where a period of insurance or residence which is completed in accordance with compulsory insurance under the legislation of a Member State coincides with a period of insurance completed on the basis of voluntary insurance or continued optional insurance under the legislation of another Member State, only the period completed on the basis of compulsory insurance shall be taken into account.
4.   Where a period of insurance or residence other than an equivalent period completed under the legislation of a Member State coincides with an equivalent period on the basis of the legislation of another Member State, only the period other than an equivalent period shall be taken into account.
5.   Any period regarded as equivalent under the legislation of two or more Member States shall be taken into account only by the institution of the Member State to whose legislation the person concerned was last compulsorily subject before that period. In the event that the person concerned was not compulsorily subject to the legislation of a Member State before that period, the latter shall be taken into account by the institution of the Member State to whose legislation the person concerned was compulsorily subject for the first time after that period.
6.   In the event that the time in which certain periods of insurance or residence were completed under the legislation of a Member State cannot be determined precisely, it shall be presumed that these periods do not overlap with periods of insurance or residence completed under the legislation of another Member State, and account shall be taken thereof, where advantageous to the person concerned, insofar as they can reasonably be taken into consideration.