Why are cels cut

That usually means someone at the studio screwed up the color somewhere during the painting process. Since cels are painted on the back, it is difficult to correct these errors, so they paint on the front. So if someone paints a Super Saiyans eyes black instead of blue, they'll paint the blue on the surface of the cel to fix it. If it's a bigger error, a correction layer may be made where the new painted area is on an entirely new sheet of acetate which is placed over the original.

Mine are usually small shading errors where they used the wrong shade of paint and fixed it by painting on the top of the cel with the correct color. It's not that noticeable unless you look at it on an angle and can see the matte surface and raised area of paint :)

Ahh ok, very interesting :) Ive only been collecting cels for under 2 months so thats a new thing to learn :) So it shouldnt put me off bidding i guess? I just didnt want a collector to have done anything to it ha

Not really...it's not ideal but it's never really bothered me. If it's enough paint, it can cause puckering on the cel bag front though, but only after several months or more. Usually the puckering is only on the back since that's normally the place where the chemically active paint is so when paint is on the front, it's only natural that it happen there too. Switching the bag occasionally will fix that. Just basing this on my own experience tho, I've only had one cel with enough correction paint for this to happen :) And yeah, it's nothing a collector would have done. It's just the cheapest way to fix that sort of production error ;)

I looked at some of the cels up for auction and there are a lot that say traceline corrected. I know some collectors may put another layer of acetate over the cel and correct the lines with a fine marker, but these cels don't have crisp enough lines to make it look like that's the case. If it's just corrections, I'd say it's paint on the top of the cel.

Traceline corrections sounds like something that would be done to counter fading but I really don't know for sure, nor can I always trust google translate :/ My best guess, is that the trace line areas that are randomly very unfaded, were corrections that were made by the studio after the initial trace lines were made and maybe weren't solid enough for their liking. I hear Toei used to just Xerox their lines, hence all the fading years later. So if they did corrections with a better ink, those maybe were more resistant to fading and account for some lines that are really dark despite all of the other lines having faded away. So the only drawback with those is no uniform fading, haha.

I've seen alot mention traceline corrections to, good to know its not to do with the collector thanks!
If its anything the studio did i'm totally fine with it, personally I dont mind line fading, cels are a product of their time and the fade just reprsents their age,
I do much prefer them not being cut, i love the studio markings and sequence numbers to still be there