不知道是不是這樣 -- I think you can keep as many leaves as you want if you can:
1) keep the cutting moist enough so that it won't dry out;
2) keep the germ away which will rot the cutting(usually by adding germicide into the mist and use sterilized rooting media, usually not soil as seen in your pics) before the cutting take roots.
Hence, usually only keep 1 leaf to keep the cutting active and not need to spread water too often and use a sterilized rooting media like pearl stone etc to put the cuttings in. the weather is getting hot now but I think still can root. Last year I have got some rose branches from England and they still can root properly with the method above.