ExcelBanter - VLOOKUP & Dates: Why is this Formula working?

Okay: 2 sheets
sheet1: called Nationality
Sheet2: called Graph

Sheet 1 consists of a table. Column A4:20 is various nationalities.
Columns B3-M3 are months of the year, with column B starting with JULY
Under Month are various percentages corresponding to nationalities for that
Month.
Cell I1: named MONTH. format of cell is general. Cell K1 is a date. Any
date can be entered, such as Dec 05.
at the bottom of this page is a graph reflecting nationailities, and the
graph
changes DEPENDING on the date entered in K1. Example: enter Dec 05 and the
nationality stats for the month of Dec show on the graph. Enter June 05 and
graph shows nationality stats for June.

Sheet 2 (called Graph) has a table
A4: A20 are nationalities
B3: cell is named PERIOD and C3: cell is named YTD for the graph
Formula in B4 is
=VLOOKUP(1,Nationality!B4:M4, IF(MONTH(date)6,MONTH(date)-6,MONTH(date)+6))
under column YTD formula is simply
= nationality!O4
I could just copy and use this existing Graph and worksheets. My problem is
that my year commences in JUNE and not July and if I merely change Column B3
(on nationalities worksheet)to June it no longer registers correctly.
Does this explain in enough detail. i am desperate to use this worksheet
and graph, but cannot understand how it is reading the date and how to get it
to commence in June. i have checked everywhere to see if there is a formula
I am missing that would explain something else.