How do indices "gisaid_epi_isl" and "genbank_accession" used in the nextstrain pipeline?

Hi. I am new to NextStrain. And I have a bunch of data, which is formatted as the following. I was particularly interested in the Accession ID part.

I was thinking to adapt the ID part to use NextStrain pipeline. I was wondering, would it be good if I only consider the GISAID sequences data to use NextStrain. Would this make a difference?

nextstrain primarily uses the strain name to identify sequences. You can use any data source and any set of accession numbers if you want.