#1 - Since you see it practically everywhere, 
I'm 99% sure that the orange "Spot Sale" icon 
simply means that it is available for sale on a 
first-come, first-serve basis only.  As you 
browse a little bit, you will notice that items 
on hold have instead a blue hand symbol (which 
obviously means "on hold").  It's interesting to 
note that items already sold can still have 
the "Spot Sale" icon.  In any case, I'm pretty 
sure that no discount is being offered whenever 
you see that icon.

#2 - I don't really know, but it's very likely 
that animators simply forget little details in 
the rush to produce episode after episode.  As 
long as animations are organized enough (or at 
least the studio can track down misnumbered 
sequences fairly easily), it's easy to imagine 
that an animator may not bother correcting a 
layout in favor of slaving over the next one.

#3 - I'll e-mail you some likely probabilities.