IIRC, FORLAB found that specific sections of an identified legitimate BC were proved to have been used as the basis of the forged BC, apparently using electronic cutting and pasting.
>> an identified legitimate BC were proved to have been used as the basis of the forged BC
No doubt in my mind that is fact.
A mechanical stamp was used for the serial numbers. And the top serif in the 1 digits have something of an elongated bullnose shape — probably to retain ink from the stamp pad. The forged 1 digit, on the other hand, has the classic pattern of a rasterized font character.