It's kind of confusing because it depends on how you phrase it with percentages.
"The number of cores in the PC went up by 50%" means "there are now 1.5x as many cores"
However, "the number of cores in the PC is 50% what is was last year" means "there are now .5x as many cores"
In this case 200% is fairly unambiguous, but imagine a phrase like "scaling community 50% per year" which could mean different things depending on the direction of the scaling... I think it's more intuitive to use a multiplier: "scaling community 3x bigger per year" makes it easy to visualize an online community tripling in size every year.
For anyone else that got tripped up... 1x to 3x is 200% growth because you don't get to count the original 1x