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I think you may be exaggerating slightly the peculiarities of legal English. The normal phrasing is, for example "This complaint is about a folder, which folder went missing on Tuesday last..." So which is natural and normal; it's folder that is unnecessary padding/zealous for clarity, as you prefer. The difference from your example is the difference between 'the folder which went missing' and 'the folder, which went missing,' ; minute, but possibly important.