The onBeforeCornerExport event is fired during image export. It lets you customize the appearance of the upper-left corner of the Gantt Chart component.
Available since version 2023.1.5529.
DayPilot.Gantt.onBeforeCornerExport(args);
dp.onBeforeEventExport = function(args) {
args.text = dp.startDate.toString("yyyy");
};