FAQ: If my input is <5ug and therefore use 0.5 ul of  3' SR Adapter 3, SR RT Primer 3 and 5' SR Adapter 3, instead of 1.0 ul, my total volumes for each reaction will be short by 0.5 ul. Should I replace that lost volume with water?

You can replace that lost volume with 0.5 ul of the included Nuclease-Free water, but not replacing it has no impact on reaction efficiency.