Okay, keep in mind that my knowledge of Lawson to this point comes from the iSeries world....
On iSeries there is an AP161X file member created for every run of AP161; so when we send our data to our VAN we ftp the last file member created. And if an ftp fails we can go back and pull that data by member number if needed.

So the questions is... How is the data from AP161 runs saved in the Unix world?

Lawson support answered my question....

These files are located in %lawdir%/productline/work/AP161ELECTPMT directory, for remit it's the same directory - but AP161ELECTREM for the remit.

Also,

The file has the same name everytime you run AP161 unless you override it in the job parameters.