I presume you are referring to the white spots as the arrows below on the picture show...????
print job runs happen over hours and hours...Ink dries and becomes tacky and not as flowing as should be...Most large not inked spots can be caused by pieces of paper adhering to the plate not allowing ink to be printed until found and removed or falls off.
Yes, sorry that is exactly what I was referring to when I said "vacations" in the colour. It is a term used in tattooing (I am a collector of those as well haha) when bits of colour are missing in an otherwise solid colour area. Since stamps are new to me I am not sure if there are always specific terms for these things.
So basically those are completely random. I am assuming then that maybe the fact both of those I showed have the marks around the curl of the C, it is probably just an area that is prone to holding the bits of paper or clumps dried ink that you speak of rather than a "mistake" persay?