I think most people would call a production cel that later gets used for merchandise a hanken cel. I would agree with this. I do have a few production cels that were later used this way. As a practical matter I have kept them in their respective sections instead of moving them to my hanken section since none of them were used for high profile items.
As for trace lines being called hankens. I think this would still be appropriate; function determining the type of cel. Since many newer shows are CG, the lines are all that remain of what would have been a hand painted cel in earlier years.
I am not sure, but I see it as a progression over time. Before the copy machine was invented and became commonplace, all cels had hand painted/inked lines regardless of use. As the copy machines became more prominent in the 1980s, most cel lines were xeroxed since it was a lot cheaper and faster to do it this way. Hankens where line quality was a lot more important were still hand inked for a lot longer. Eventually even hankens had copy lines though I heard that a higher quality of ink was used. Once CG took over and high quality images could be produced on the computer, hankens were reduced to lines only and then to sketch only.
I have no idea if test cels have sequence numbers on them. I do not own any. I do have a few cels and backgrounds that were originally made for shows, but were later edited out. I would refer to these as preproduction cels/backgrounds. All of these preproduction pieces are numbered just like my production artwork.
The four backgrounds from Mirage of Blaze of the bottom of this page are examples of incorrect backgrounds that were edited out.
http://itamejihada.net/backgrounds/mob/mob.tv13.5.html
This is a Last Unicorn background that was edited out.
http://itamejihada.net/backgrounds/lu/lu1c.html
This is a Last Unicorn cel that was later edited out.
http://itamejihada.net/cels/lu/lu2b.html
There are a few others in my gallery. Over the years I have also had others that have come and gone. I generally don't separate them out since I pretty much consider them as legitimate as other cels. If anything, I find them very interesting because they provide a window into how the show could have been.
Like I said before, I do not know if test cels have numbers or not. One thing I notice is that they tend to be nearly perfect shots of a character. They are well-centered and show the entire face/body. Sometimes they show the characters in different colored clothing since they are testing out different looks. For example I seem to remember that someone here has a test cel of Hinoto (X/1999) with purple eyes instead of red.
