create_data followed by a directory will process the proposal file (generally a 5-digit string followed by ‘.prop’) in that directory. The proposal file contains the names of the FITS files to be processed and the relationship between the exposures, allowing a unique numbering scheme.
Each FITS file referred to in the exposure will be processed to make a Level1b format JWST dataset with the pixel data flipped and/or rotated to make it conform to the DMS coordinate system, in which all imaging data has roughly the same orientation and parity on the sky.
The 5-digit string is used in the name of the Level 1b product, in that file 12345.prop will make data of the form
The numbers that fill in the other letter spaces come from the structure of the proposal file, which is a sequence of nested levels. As each level is repeated, the number assigned to repesent that level increments by 1.