Not sure I can give you correct answer. But I can give you answer from my point of view. When you add file in node, it will announce you have this file to network. So in your case, both node-A and node-B announce they have this file. When you get this file in node-C, usually you will get chunks from both node-A and node-B simultaneously, which depends on routing. In one IPFS node, there's only one copy of same content if you have same file with different file name.