Dates entered with a custom format of 'd-mmm-yy' correctly display in Excel in a format similar to '8-Apr-14'.
If the locale on the OS is then changed to English (UK), the cell on screen then is displayed '08-Apr-14'.
In this scenario, the GetCellText APIs still return dates formatted as '8-Apr-14'.
If the Excel Engine had localization support for English (UK), the dates returned from GetCellText would be returned as what is seen onscreen '08-Apr-14'