It seems that the 0.7.4 WoT client will play old replays, it will give you a warning that the client might crash while doing so, but it will play them. 0.7.4 client is verified to play 0.7.3 replays, and looks like it will play 0.7.2 replays as well. Why WG didn't put this in the patchnotes is beyond me...

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