Using TabOrder to identify controls

I have a UserForm with 12 TextBoxes the values of which I need to enter into a WorkSheet.

I have given these controls tab indexes from 0 to 11.

I have been trying, unsuccessfully, to write code that will do the transfer on the lines of:-

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I know that I could accomplish this by using a control name such as "TextBox" & i but this way is not available to me as it is being used already for another purpose.
I hope that somebody will be able to put me on the right path.
John

I have followed your suggestion and used the Tag property with code as follows:-

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All works well till Ctrl.Value = Sheets("Customer_Complaints").Range(Cells(RowNo,a+1)).value
This gives an Application defined or Object defined error. Ctrl.Tag is what I expected, but I suspect that Ctrl.Value might be wrong.Can anyone help please?
John