Bar-raiser program didn't have a feedback loop to track its effectiveness. Bar raisers periodically met to discuss topics related to hiring and increasing interview bandwidth but we didn't evaluate the process as such.
That said, the program (like any such program I guess) didn't scale well with the immense pressure on increasing the head-count which in itself was a result of delivering more. Hiring managers and recruiters (who are incentivised to hire more) would rig up interview loops in a way to get their candidates through.
The program itself came under increasing scrutiny (I guess for the right reasons) as being too restrictive. I distinctly remember period between 2008-2012 they hired at a blistering pace, all over the world. In fact in Seattle when they moved into SLU campus the buildings went from empty to nearly 100% occupancy in a matter of year or so. You could even see it based on the number of product launches from 2012 onwards (AWS, the hardware products, new country launches etc.,).
And now Amazon is such a behemoth that it doesn't even make sense to speak about it or analyse it as a single entity anymore. My prediction is in 5-8 years it'll be broken up into at least three companies under Amazon as a holding corporation --- cloud, retail, and consumer devices.