Probably just that the two aircraft were certified on different days, by different pilots, under different certification standards.
Determining Vne experimentally is - by its definition - somewhat subjective. Not many TPs of today are prepared to over-speed the aircraft until it suffers some sort of structural failure.
Nowadays, the engineers have an accurate idea of what will cause the limitation - and so certification tests are designed to explore that limitation, rather than actually exceeding it to failure.
For example, if the engineers estimate that wing-flutter will occur at speed X, the TP might perform a series of tests with incrementally increasing airspeed, with an oscillator attached to the wingtip, designed to induce flutter at a lower airspeed than might be encountered in still air. Eg as in this photo:
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So as you can imagine, there is a lot of scope for experimental differences in two different certification procedures.