Yes—multiple internal revisions are entirely plausible, even when a camera model looks the same externally. As with many mass-produced products, manufacturers often make running changes during production without changing the model name or outward appearance. If both cameras are definitely Ricoh 500G bodies, the fact that their internal parts differ is strong evidence that more than one internal version exists. That means donor parts may not always interchange directly, so matching by production details or comparing assemblies carefully before swapping parts is wise.