No, we don't know why. All the hx35 maps show 50-53 lbs/min. This one
here is an hx35 compressor map verified by a turbocummins group as coming from a holset engineer. This one is all over the web. Those rpm curves are not corrected.
And here...
...is another one from the
Holset Hx35/35W Product Information Sheet. I think to which you were referring. 0.38kg/sec X 60 X 2.2046 = 50lb/min.
Here is
another from Morphius, who started these threads. This is from a Cummins engineer as well. You can take the cfm, lb/min, kg/sec info from the othe holset printed maps and come up with a conversion of their cfm to lbs/min based on their temp used of 85*F and 14.425psi atmosphere. The conversion is CFM X 0.07333 = lbs/min. This 705cfm map converts to 52lbs/min.
The official one is for an hx30e compressor wheel showing 53lb/min. The part numbers are the same and the same compressor housing is used between the 2 turbos. And you can see the first map and this show very similar topography: