In 2011 - 388 billionaires own the same wealth as the poorest 3.6 billion people..
In 2012 - they were 150
In 2013 - they were 92.
In 2014 - they were 80.
In 2015 - they were 62.
In 2016 - they were only 8. (1)
I do not know any older statistics, nevertheless I bet that the accumulation has passed to the top speed with the fall of the Berlin Wall, in 1989, when the competitor of neoliberalism has disappeared.
(1) Update 5/7/2019:
It may have been a mistake in the wording, because in report 2019, l'Oxfam mentions:
43 people in 2017,
26 people in 2018.