When you come to order image files, drawings, prints or canvases you will use the numbers we have used to catalogue Bob's work.
The majority of drawings are numbered based on the envelope system Bob set up. Envelopes are designated E1 to E306 and within each the drawings are numbered from 1 to 50, starting with the image Bob put on the top of the pack. So we have numbers like E12 34 which is the thirty fourth drawing in the twelth envelope.
You will be able to refer either to a specific numbered image in a post or to one of the 50 images in the Envelope Overview.
Paintings are numbered based on the batches in which the first photographs were taken. Within the batches two digits refer first to the row then the number in the row. So B12 34 refers to the fourth canvas in the third row of canvases in the twelfth batch.