These methods no longer have effect when attached to SheetView. This is because while adding span cell, its location will be checked against other features like Table, ArrayFormula, and if they are called directly from the model, the check against other features can't be made, which can result in wrong data.

For a case where span model is already attached to SheetView, it is recommended to use SheetView.MoveRange/SwapRange/CopyRange methods to ensure the data integrity of all features.

DefaultSheetSpanModel spanModel = fpSpread1.ActiveSheet.Models.Span as DefaultSheetSpanModel;
spanModel.Move(0,0,4,4,2,2); //has effect and is recommmended

For a case where span model is stand alone and not attached to SheetView, the above methods still have effect.

DefaultSheetSpanModel spanModel = new DefaultSheetSpanModel();
spanModel.Move(0,0,4,4,2,2); //has effect

When stand alone DefaultSheetSpanModel is created and assigned to SheetView, invalid data of span model will be ignored and only valid data will be added. For example,

fpSpread1.ActiveSheet.AddTable(1,1,6,6);
DefaultSheetSpanModel sheetSpan = new DefaultSheetSpanModel();
sheetSpan.Add(0,0,2,2);
fpSpread1.ActiveSheet.Models.Span = sheetSpan; //contains invalid span
fpSpread1.ActiveSheet.GetSpanCell(0,0); //returns null