Assuming UK/Australia pattern date format is used where you live the following will give you the last 12 months from today (page 6 of Paul's document). If you use US format dates then see the preface of Paul's document for the conversion. If you want the last 12 months add a minus sign before the delay values e.g..
{QUOTE{SET Delay -1}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -2}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -3}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -4}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -5}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -6}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -7}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -8}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -9}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -10}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -11}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
{QUOTE{SET Delay -12}{SET m{=MOD({DATE \@ MM}+Delay+11,12)+1}}{SET y{=INT({DATE \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}}"{m}-{y}" \@ "MMMM yyyy"}
which produces
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
Copy the field code sequence from Paul's document or use
Import and export field constructions as text to restore the fields.