You do not need four part programs if you are only using one tool.
The main program selects the work zero then calls the part program:
%
O0001 (MAIN PROGRAM)
G54 M98 P0010
G55 M98 P0010
G56 M98 P0010
G57 M98 P0010
G54
M30
%
%
O0010 (PART PROGRAM)
etc
M3 S1500
G0 X18.2972 Y-0.4192
G0Z0.5308
Z0.1600
etc
G53 G00 Z0.
M99
%
You will notice I added G53 G00 Z0. to the part program. This is so the tool is lifted clear before moving to the next part. Also I changed the order in which the tool approaches the part; it moves first to the X and Y position then down to the Z. This means it is less likely to hit clamps, etc, sticking up higher than the part.
If you are using two tools the main program becomes;
O0001 (MAIN PROGRAM)
G54 M98 P0010
M98 P0020
G55 M98 P0010
M98 P0020
G56 M98 P0010
M98 P0020
G57 M98 P0010
M98 P0020
G54
M30
And you have a Part Program, O0020, for the second tool.
An open mind is a virtue...so long as all the common sense has not leaked out.