Anon, the concept of chozer v’niur goes as follows:
When something is batul, nullified, in a mixture, this can happen through having 60x the volume of the nullified item, or the majority, depending on the case. Sometimes you need 100x..
Typically, the concept of chozer veniur means that if there was enough to nullify the item, but then more of its own substance was added, the material that was previously nullified is counted with the new stuff.
For instance, a pot has 122 ounces of chicken, and one ounce of chazir falls in. No problem, because you have 60x the chazir. But what happens if subsequently, 2 more ounces of chazir fall in – each one by itself would be batul, but when you add them together, you get 3 ounces, which would require 180 ounces of chicken to nullify. Do we say that what’s done is done, and the first ounce is as if it’s not there anymore, or do we say it is “revitalized” by the additional ounces.
That’s chozer veniur.
Reb E is saying that if the chometz was batul before pesach, do we say chozer veniur because now there’s a new issur that previously was not there, one which is not subject to bitul, as chometz on pesach is never batul, even in a mixture of 10000x itself. Do we say that the chometz should be looked at as gone completely, since it was batul before pesach, or do we say to look at it as still existing, and subject to the current judgement of not being batul no matter how much there is against it.