You will find the among some KJV-Onlyists the assertion that the 1611 KJV Bible was directly inspired by God. That cuts away any need for them to explain why the KJV can be considered the infallible word of God while its immediate predecesors should be viewed with scepticism.
For example, Peter Ruckman:
The text of the A.V. 1611, in Genesis 27, is the inspired infallible
text, preserved without error.
The Holy Spirit has thrust Himself into the AV committee of 1611 and
The “truth” is that translations can be given by inspiration.
Now, it should be pointed out that he seems to make some distinction between "inspired" and "given by inspiration":
What version of the Bible was the inerrant, infallible, inspired
translation prior to the AV1611?” Answer: Who cares? Ask the people
that read it. We believe the one we have is infallible and inerrant
and is “given by inspiration” (not “inspired”).
but it's hard to see how that distinction makes any difference.
The only conclusion that seems possible is that the KJV-Onlyist believes that the earlier manuscripts used by Erasmus, Beza, Stephanus etc. were good, but probably not perfect. However when the time came to translate those documents into English, the Holy Spirit supernaturally guided the translators to choose the correct words from their available manuscripts, and replace any errant words with inerrant words as the Spirit inspired them.
There is also a view (put forward, for example, by David Stewart) that the many versions that led up to the final KJV translation represent a fulfilment of Ps. 12:6, where God's word is likened to gold refined seven times.
Personally, I think the claim that the KJV is the result of a supernatural re-inspiration of the translators by the Holy Spirit is an indefensible claim entirely without scriptural warrant. But if one accepts that as their foundation, it allows them to easily sweep aside questions of which older manuscripts were accurate. Like Peter Ruckman says, who cares what God's inspired word was before 1611? Not him.