Combining the flight records

Three youth groups tested the same four paper-glider designs, and I offered to combine their results. The North group measured each distance from the launch line to the glider's nose, whereas the West group measured to its tail. North recorded the first flight of each design, but West selected the longest of three attempts. The East group had copied the designs onto thicker paper because the usual sheets had run out. On one results page, two rows were both labelled Design 2 and there was no row for Design 3. Three flights beyond the end of a ten-metre tape were recorded only as 'more than 10 m'.

Describe the difficulties of combining the glider flight results. Brief quotations may be used to support your points.