>I need to programatically find the date of the last day of the previous 11 months based on the current date.

this any good ?

local d, i
d = date()

for i = 1 to 11
	d = bomonth(d) -1
	? d
endfor

*---------------------------------------------------------------------------
function	bomonth(d)
	return d+1-day(d)
endfunc
*---------------------------------------------------------------------------
function	eomonth(d)
	return gomonth(bomonth(d),1)-1
endfunc
*---------------------------------------------------------------------------