Quoting floor preparation

I am about to tile a bathroom floor. This previously had carpet down and on taking it up I am left with an extremely flat flooring grade chipboard floor which seems to have been laid over the old floorboards when the property was renovated about 20 years ago. It says in the sticky for this forum that when tiling over a chipboard floor it should be covered with plywood. Would this still apply in this case Thanks in advance for your time.
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