BUFNO can be taken from the JCL, File statement or the Options table. Whether the file is input and output determines which BUNFO parameter will be used and the order of precedence.
Easytrieve parses the FILE statement differently for INPUT files and OUTPUT files.
For INPUT files, BUFNO will come from the JCL.
If not in the JCL, Easytrieve checks the FILE statement.
If not there, Easytrieve gets it from the options table.
For OUTPUT files, Easytrieve ignores the JCL and check for the BUFNO parameter on the FILE statement.
If it is not there, Easytrieve uses the BUFNO from the options table.