What is the discrepancy between the 'Date of Issue' on the TM30 spreadsheet and 'Date of Arrival' on the paper TM30?

In column H of the TM30 spreadsheet for online uploading, the data is headed, “Date of Issue”.

On the paper copy of the TM30, the corresponding field is headed, “Date of Arrival”.

I will add the date of issue of my passport on the spreadsheet, out of interest has anyone had any clarification of the discrepancy in these two documents?