Problem interpreting ambiguous Excellon drill data

gistfile1.txt

=== border.gko === Just shows outline of board so we can get our bearings.

G04 This is an RS-274x file exported by *
G04 gerbv version 2.6.0 *
G04 More information is available about gerbv at *
G04 http://gerbv.gpleda.org/ *
G04 --End of header info--*
%MOIN*%
%FSLAX34Y34*%
%IPPOS*%
G04 --Define apertures--*
%ADD45C,0.0039*%
G04 --Start main section--*
G54D45*
G01X0075595Y0061827D02*
G01X0075595Y0098047D01*
G01X0122643Y0061827D02*
G01X0122643Y0063795D01*
G01X0122643Y0090764D02*
G01X0122643Y0098047D01*
G01X0075595Y0061827D02*
G01X0122643Y0061827D01*
G01X0122643Y0063795D02*
G01X0124217Y0063795D01*
G01X0124217Y0063795D02*
G01X0124217Y0090764D01*
G01X0122643Y0090764D02*
G01X0124217Y0090764D01*
G01X0075595Y0098047D02*
G01X0122643Y0098047D01*
M02*

=== 4holes.gtl === 4 0.205" (5.2mm) holes lifted from the customer's .gtl file

G04 This is an RS-274x file exported by *
G04 gerbv version 2.6.0 *
G04 More information is available about gerbv at *
G04 http://gerbv.gpleda.org/ *
G04 --End of header info--*
%MOIN*%
%FSLAX34Y34*%
%IPPOS*%
G04 --Define apertures--*
%ADD35C,0.2047*%
G04 --Start main section--*
G54D35*
G01X0079851Y0093323D03*
G01X0120032Y0093323D03*
G01X0085965Y0063992D03*
G01X0113918Y0063992D03*
M02*

Location of holes according to gerbv (inches):

  7.9851, 9.3323
  12.0032, 9.3323
  8.5965, 6.3992
  11.3918, 6.3992

There's an obvious correlation between these locations and what's in the file.  It's an absolute coordinate system.

These locations in mm:

  202.82, 237.04
  304.88, 237.04
  218.35, 162.54
  289.35, 162.54

=== 4holes.txt === 4 5.2mm (0.205") holes lifted from the customer's .txt file

M71
M48
T12F00S00C5.200
%
T12
X009734Y00055
X002634
X011287Y008
X001081
M30

File is implicitly in metric because of M71.  Y value stays the same between hole 1 and hole 2, and hole 3 and hole 4.  

Is this some sort of relative system?  
Y difference in inches: 9.3323"-6.3992"=2.9331".
Y difference in mm: 237.04042mm-162.53968mm=74.50074mm.

How to correlate this with above?

How is position expressed?