Cells with special number format interpreted as date

If a cell has a custom number format (in my case Y000000), the stylesheet parsing (called in excel.py, line 279) recognises and registers this as a date format. Later-on, in worksheet._reader.py, line 200, the numbers are converted to dates as a consequence of this:

if style_id in self.date_formats:
    data_type = 'd'

I have a hard time getting back the correct number, even using the to_Excel function, that gives me e.g. an offset at 60. I realise the challenge is really Excel's sloppy handling of dates and date-times. But could there be a flag given to load_workbook that preserves numbers as numbers when datatype is n?minimal_y_formatted_in_A1.xlsx

Attached an Excel file with only cell A1 containing data. The cell contains the number 60, formatted as Y000000, hence displaying Y000060 in Excel.