The sample spreadsheet is what is left after I have deleted all the other data that has no bearing on THIS question.
Cells highlit in yellow in column A viz, 3, 8,10, 11 and 17, are resistant to format painting, or any other reformatting I have tried - but it depends on the year. They look the same as all the other entries because I have edited them to be text - using the apostrophe prefix. If I remove the apostrophe e.g. in cell 11, the format becomes 07 10 16. If I drag cell 9 onto cell 10 it becomes 07/10/2017 - if I change 2017 to 2016, the format becomes as in cell 11. How can I remove this stubborn inconsistency ?