Paper or Saran Wrap will shim the caps that are too loose.
As for why some are tight and some are not... I see this on my 3d printer, how fast the plastic cools can effect how much shrinkage there is. On an open printer, with no enclosure, simply opening a window or door can make visible changes in the object as some layers will shrink more than others. The same can happen by changing the temp they are molded at, some of my ABS needs 227c, another prefers 119c, not only can different manufacturers effect this, coloring can too. My bet is that they were done at different times, and a temp was set wrong.
Looking closer at the caps, it looks like they were cooled at a different rate, or on a different mold.