given the limited scope of files in the direcctory... not sure why it was necessary to use grep, instead of the built in glob?

  ls dataset-directory | egrep '\d\d\d\d_A.csv'

which FWIW wouldn't even work, on multiple levels: you need -1 on ls and no files end with A.csv

  vs

  ls -1 dataset-directory/*_A?.csv

ref: http://man7.org/linux/man-pages/man7/glob.7.html

Update: apologies, apparently my client cached an older version of this page. at that time the files were named A1.csv and A2.csv