If dry coverstock only is in contact with the lane, there can't be carrydown. You only get dry coverstock contact with track flare.
How much a ball flares or not just determines how the carrydown is deposited on the lane. Not whether there is or isn't any carrydown.
This is a image from Kegel showing carrydown produced by flaring and non flaring balls.
Those little strips can build up over the course of a few games, add those to the long strip carrydown left by low flare balls and the backends can tighten up a lot.
Oil volume and Coverstock types (Charlests rate of oil absorption) will also affect how much carrydown there is.
Plastic balls will deposit the most, because all the oil just sits on the balls surface. Resin balls will deposit less, because they absorb the oil into the coverstock very fast.
Something to note also about resin balls is, the amount of oil you see on a balls surface when it comes back. Is less than what you would have seen on it when it first came out of the oil on the lane, because that oil will be absorbed by the time it gets back to the return.