It is what it is. At least the cel hasn't yellowed yet. I've had that happen to some. I would use a photographic process (called a PMT) to transfer the linework to the acetate and that requires chemicals and washing etc. Before I was at Future the place I'd use was really good...

...but when I moved down to Bath, even though (luckily) Future had a machine to do it (a holdover from the pre-digital days) I had to do it myself and the chemicals were a bit old. Those pieces have suffered the worst.