If I go on adjusting a psd-file which has been flattened, will the file´s image quality go worse?
Basically any Adjustment will be detrimental – but usually the deterioration with Adjustments that are not extreme is (close to) unnoticeable.
Working in 16bit can help keep the detrimental effects smaller than when working with 8bit images.
I´m pondering if I have to go back to the file with layers, or can I continue with the cropped file and make new adjustment layers on this flattened image.
Do you get banding?
It’s your image, so it’s up to you to decide if the image deterioration is so bad as to warrant starting over.
Why did you not continue working with the layered file anyway?
Yeap, I think I might have to go back to the layered file. I made some mishaps in my workflow which was very complicated, highly processed image file...and made even further changes to the image after flattening and cropping, hard to explain, but I have to do a lot same work again, to get a good new version with different curves and saturation etc. Sometimes Photoshop-workflow can get quite complex and if you don´t stay very organixed and pre-planning...ugh...