That's different. In which case, I would eliminate the commas and format accordingly. Here is proof that you can run in Scripts - Background:

var oString = '20,210,526';
var nString = oString.replace(/,/g, "");
gs.info(nString);
var yyyy = nString.slice(0,4);
var mm = nString.slice(4,6);
var dd = nString.slice(6,8);

gs.info(yyyy);
gs.info(mm);
gs.info(dd);

var gd = new GlideDate();
gd.setDate(yyyy + '-' + mm + '-' + dd);
gs.info(gd);