I believe the chart was created by someone on this forum. It is based on the information on this site:
http://www.twf8.ws/new/tech/shocks/shock.htm
Reviewing the info on the above link, it seems the conflicting data (that goes against the chart seen on this page) are "unofficial conversion values provided by Gene Hickerson USA":
Cts Losi WT Associated WT
100 10 7.5
150 15 12.5
200 20 17.5
275 25 22.5
300 27.5 25
350 30 27.5
400 32.5 30
425 35 32.5
450 37.5 35
500 40 37.5
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It's not mentioned how these figures were obtained, so for now I'm going to trust amain and the figures taken with accurate equipment which both state that Losi is slightly heavier.