I can personally attest to the percentages being bogus. I have a mining rate of 99% on some items. To fail THREE times in a row is a one in a million chance. To have a 3x fail happen twice in a 20 minute gathering session is highly unlikely, but it happened to me.

Also, while farming another item from a Lv50 node, I had a listed success rate of 93 percent. According to my logs, I attempted gathering 2,813 times, with 2,430 successes for an actual rate of 86.4 percent. With a sample size that large, this is clearly an indication that the listed success chance is, most likely, just pulled out of someone's ass.