Mistake ?

[Kagelmacher]

In this part of the book : http://cnp3book.info.ucl.ac.be/2nd/html/principles/reliability.html#go-back-n-and-selective-repeat. You said : "Consider for example a go-back-n receiver that received frames 1, 2 and 3. It sent OK1, OK2 and OK3. Unfortunately, OK1 and OK2 were lost. Thanks to the cumulative acknowledgements, when the RECEVEIR receives OK3, it knows that all three frames have been correctly received.".
Would not it be ? : "..., when the SENDER receives OK3, ..."