I wonder where the line is between being a copy of another design and not. Just in this 99designs logo store alone we have examples of thousands of logo designs

I wonder where the line is between being a copy of another design and not. Just in this 99designs logo store alone we have examples of thousands of logo designs. If someone where to sit down and make a new logo design, what are the odds it would be noticeable similar to one of these? In programming, we have "design patterns" and such, that no-one would argue "hey, you copied me!" over. What about design patterns in logo design? I'm not a logo designer, but I find it hard to believe that each and every logo design is, or plausibly could be, designed entirely from scratch.