Even Iraneus had said this corruption is common during his time.
I do not know how it is that some have erred following the ordinary mode of speech, and have vitiated the middle number in the name, deducting the amount of fifty from it, so that instead of six decads they will have it that there is but one. [I am inclined to think that this occurred through the fault of the copyists, as is wont to happen, since numbers also are expressed by letters; so that the Greek letter which expresses the number sixty was easily expanded into the letter Iota of the Greeks.] Others then received this reading without examination; some in their simplicity, and upon their own responsibility, making use of this number expressing one decad; while some, in their inexperience, have ventured to seek out a name which should contain the erroneous and spurious number. Now, as regards those who have done this in simplicity, and without evil intent, we are at liberty to assume that pardon will be granted them by God. But as for those who, for the sake of vainglory, lay it down for certain that names containing the spurious number are to be accepted, and affirm that this name, hit upon by themselves, is that of him who is to come; such persons shall not come forth without loss, because they have led into error both themselves and those who confided in them.
http://www.earlychristianwritings.com/text/irenaeus-book5.html
I do not know how it is that some have erred following the ordinary mode of speech, and have vitiated the middle number in the name, deducting the amount of fifty from it, so that instead of six decads they will have it that there is but one. [I am inclined to think that this occurred through the fault of the copyists, as is wont to happen, since numbers also are expressed by letters; so that the Greek letter which expresses the number sixty was easily expanded into the letter Iota of the Greeks.] Others then received this reading without examination; some in their simplicity, and upon their own responsibility, making use of this number expressing one decad; while some, in their inexperience, have ventured to seek out a name which should contain the erroneous and spurious number. Now, as regards those who have done this in simplicity, and without evil intent, we are at liberty to assume that pardon will be granted them by God. But as for those who, for the sake of vainglory, lay it down for certain that names containing the spurious number are to be accepted, and affirm that this name, hit upon by themselves, is that of him who is to come; such persons shall not come forth without loss, because they have led into error both themselves and those who confided in them.
http://www.earlychristianwritings.com/text/irenaeus-book5.html