See 2.2.41.1.13 of RID:

"Classification of self-reactive substances not listed in 2.2.41.4, 4.1.4.2, packing instruction IBC520 or 4.2.5.2, portable tank instruction T23 and assignment to a collective entry shall be made by the competent authority of the country of origin on the basis of a test report. The statement of approval shall contain the classification and the relevant conditions of carriage. [...]"

This BAM No. represents the collective entry itself - it has been assigned packing method OP6 according to 4.1.7.1.4 b) of the RID. A packing method with a lower OP number may be indicated in the approval certificate of the competent authority if the self-reactive substance meets the criteria of the Manual of Tests and Criteria, para. 20.4.2 b) only in a smaller packaging.