I have problems revising

[Kosheh]

i deleted the sign from the original author...

and tried to pass it off as your own. In the real world, this is called plagiarism and can get you in trouble when writing a paper, or even expelled from universities.
I mean this is like "fixing" a painting by covering up the original author's signature with a sticky note.
Sure, credit tags are dated, but like - people put them on the sheet for a reason.

To be honest, I wouldn't mind if our spritesheets were revised to have colored backgrounds so it's easier to copy-and-paste them into Photoshop - but you shouldn't be erasing the evidence of other people's work.  
Sure, we could do something more 20th-century, like I don't know, EXIF tags, but let's pretend it's 2003 and none of us know what that is OK