Imported .obj planes are all the same? I have a simple planes.obj file that specifies three different planes as follows.

o Plane.001
v 1760.196289 415.064117 4.388165
v 1873.999268 475.749756 4.069328
v 1774.738525 408.389893 4.310055
v 1658.910156 367.099365 4.609004
usemtl None
s off
f 1 2 3 4
o Plane.002
v 1873.999268 475.749756 4.069328
v 2020.038696 542.020508 3.850709
v 1908.386230 464.870331 4.095686
v 1774.738525 408.389893 4.310055
usemtl None
s off
f 1 2 3 4
o Plane.003
v 2020.038696 542.020508 3.850709
v 2064.233643 566.508362 3.762149
v 1948.476562 485.951721 4.011188
v 1908.386230 464.870331 4.095686
usemtl None
s off
f 1 2 3 4


When I imported it into Blender, the three planes are all the same. The demo below shows the three planes were stacked perfectly into one plane until I moved them apart.



Am I defining the planes wrongly?
you have 12 vertices, but are only using 4...
'f 1 2 3 4' is your first plane, so edit second one to read 'f 5 6 7 8' and third one to 'f 9 10 11 12'