The only 10% that W/W worries about is the first and of course ya'll know how to figure that.
Many people do percentages of their weight as small goals. Personally I just looked at 5 pound goals.
However if you started at 200 pound and your goal was 140 your 10% would be 20 pounds or at 180; 20% of your starting weight would be 40 pounds or at 160 and 30% of your starting weight would be 60 pounds or your goal weight.
If you did it as 200 again the first 10% would be 20; then if you did the 10% of that it would be 18 more pounds (giving you total of 38 lost); then 10% of that 16.2 more pounds (giving you a total 54.2 pounds lost). You would not make it to a 4th 10% at your goal.
Actually it is however you really want to do it. W/W only sets one 10% goal.
BTW all the nutritional manuals/journals and courses I have taken only address the first 10% because that makes such a difference in a person's overall health.