Date edit function not working

Hi.
I want to rename a file as "YYYY MM accounts.pdf", where MM is the month the file was renamed -1 (as I receive my accounts in the following month). So, running the rule today (in February so MM = 02) should give MM as 01. This doesn't appear to be working. Curiously the example filename in the rule editor shows correctly, but when I run the rule I get 02 (so no -1 applied). I have tried making adjustments of different magnitudes to test (e.g -2) which also does not work. Still get 02. I also tried the -1 adjustment on the YYYY and this also didn't appear to do anything.
Am I missing something?
Thanks.
I want to rename a file as "YYYY MM accounts.pdf", where MM is the month the file was renamed -1 (as I receive my accounts in the following month). So, running the rule today (in February so MM = 02) should give MM as 01. This doesn't appear to be working. Curiously the example filename in the rule editor shows correctly, but when I run the rule I get 02 (so no -1 applied). I have tried making adjustments of different magnitudes to test (e.g -2) which also does not work. Still get 02. I also tried the -1 adjustment on the YYYY and this also didn't appear to do anything.
Am I missing something?
Thanks.