6.1.1 All controlled documents are assigned a unique reference code, identification number, an alphabetic revision level and an issue date. Format is defined in Attachment #1.
6.1.1.1 Document’s revision letters starts with the letter “A” for new documents and continues sequentially up to letter Z. Afterwards, continues with double letters if necessary (i.e. …X, Y, Z, AA, BB, CC…etc.).