>I didn't and was 
>somewhat irritated that I wasn't told when I 
>purchased it.

I felt your pain, same thing happen to me before, 
bought a cel and was not told it was a repro, 
immediately noticed something was wrong when I 
received the repro cel, although it is easy to 
tell if it is repro or not when viewing the cel 
in person, it is very hard to tell from a scan.

Thankfully, stuio pierrot only used a few 
selected shots, most of these are sold at pierrot 
festivals, in a green frame, no studio pierrot 
seal, no sketch, no sequence #, and paint look 
weird, and lines is perfect, studio pierrot also 
release real production cels at festival, however 
these has studio pierrot seal, sketch, sequence # 
and paint don`t look weird as the repro.

I have saved all the images of the repro cel 
released by studio pierrot, in case you are a new 
collector and can`t tell the difference, just 
post the cel on this forum and I will give you a 
comparison with the image I saved.