我是一名天体物理科研人员以下是我论文的Introduction部分请进行润色保留文献引用：From two centuries ago until 2016 there were very few reports on quasars with velocity shift BALs eg Vilkoviskij & Irwin 2001; Rupke et al 2002; Hall et al

Over the past two centuries, there has been limited research on quasars with velocity shift BALs, as evidenced by a handful of reports (Vilkoviskij & Irwin 2001; Rupke et al. 2002; Hall et al. 2007; Joshi et al. 2014; Grier et al. 2016). Notably, Grier et al. (2016) is the only study to date that has investigated velocity shifts within a quasar sample, as opposed to individual sources. Despite analyzing a sample of 140 BAL quasar sources, the authors only identified three instances of velocity shifts