At least one in six women will be raped over the course of their lives; actually the numbers I see are usually significantly higher than this (rape statistics suffer due to extreme under-reporting).

That only holds if the fact that rapes are under-reported was not used in calculating the estimate that one in six women will be raped. The site you linked to gives no reason to think that's the case, it's pretty likely that less than one in six women reports a rape, and then estimates of reporting rate were used to get an estimate of one in six.

(Edit to add) That is, if the "1 in 6" is an actual estimate of rapes; the Eric Raymond piece Eugine Nier linked seems to indicate that there never was such an estimate, the 1 in 6 number originally also included attempted rape, and then turned into a number of actual rapes by a game of Chinese whispers.