Interpreting DCRB records:Signatures

If more than 23 gatherings (A-Z) are used, the sequence continues with AA-ZZ then AAA-ZZZ and so on. A gathering of 12 signed MMM is expressed as 3M12.

To further complicate things, some gatherings are signed with symbols (*) &/or numbers, and some use duplicate sequences of the same signature.

And 19th-century printers may have used 26 letters, which must be rendered like so: A-I4 J4 K-U4 V4 W4 X-Z4.