It makes no difference, the thrust - in order to meet the performance chart criteria should be set within the line up allowance.
Boeing simply state that setting thrust on a rolling start has a negligable penalty.
The reality is that it rarely makes any difference, but to be totally accurate that is what is supposed to happen.
Statements like set thrust by 40 or 60 knots are difficult because there is no way of quantifying where 40 or 60 knots is in relation to the start of takeoff - which means that there is no way of ensuring that the performance figures that the ops engineer has worked so hard to calculate and that you have gone to all the trouble of extracting are near to meaningless - unless you are happy to exit the end of the runway at 40 or 60 knots in the event of a reject - or are prepared to compromise your 35 ft(+gross to nett margin) obstacle clearance in the event of a go..
Like I say it is mostly semantics because it rarely makes any noticable difference in real life operations.