Has this rim strip expired? I have 2 unused rim strips. Along the edges and on the surface there are brown marks (patches, streaks, blotches). 

2 images (I cannot improve the resolution)





Observations


Both strips were stored hanging vertically (i.e. not folded nor rolled up).
When I place the 2 strips over each other, I see that the edge marks overlap, i.e. the strips have the same brown edge marks in the same positions.
Overall the rim strip is smooth. The material is not brittle. There are no scratches nor nicks.
Seems like the brown color has steeped into the plastic.
The size written on the rim tape: 32 559
There is a number which looks like a manufacture date: 06/05
Manufacturer: Schwalbe


Questions


Is this rim strip beyond its use-by-date, i.e. if I use it will it need to be replaced soon?
Perhaps an alternative question: what does a rim strip look like when it is in need of replacement?
This particular rim strip absorbs color from everything, and it is not a problem. Mine have turned green in use from something leaching from tubes.

In general, rim strip should be replaced if it splits, stretches deep into the spoke holes or exposes the spoke holes. Discoloration happens, but since rim strips aren't usually visible this is not much a problem.