The first human genome sequence was published in 2001. The reference genome has since had constant additions to it so that it can better represent the range of variations between us humans. The current version is called GRCh38. A group of researchers, led by Rachel Sherman, set out to create a pan-genome for Africa. Of the tested DNA they discovered some sections, longer than 1,000 base pairs, did not match the reference, GRCh38. They found nearly 300 million base pairs or about 10% of the reference genome. The big problem with this new information is that it can have medical consequences. Since the reference genome doesn't adequately represent certain populations, when looking for genome variations linked to conditions you are going to want a reference that's more representative of the tested DNA. By creating a pan-African genome they plan to help with this problem. 

https://arstechnica.com/science/2018/11/our-human-reference-genome-is-missing-a-lot-of-material/