for location based finding of spline points i know that you could use the find input key closest to world location node. it will actually return the closest point on the spline in terms of points. so if you were between point 3 and 4 it would return a value of 3.x where x is how far from point 3 you were, ie if you were halfway then it would be 3.5. you could then take the value and round it to get a integer that correlates to a spline point.
aside the the location use case i haven’t used the other similar nodes. i just tried location at time node with the input key location and that one seems to work but im not sure how the time works (i think its about 0.1 time per unit of distance). the input key at distance seemed to only return a 0-1 value so it may be worth playing with but not quite what you need.
