I received answer from author:
Dates in the m/d/y or d-m-y formats are disambiguated by looking at the separator between the various components: if the separator is a slash (/), then the American m/d/y is assumed; whereas if the separator is a dash (-) or a dot (.), then the European d-m-y format is assumed.
In other words I just needed to change separator from slash (/) to dash (-] and that solved my issues with “invalid” dates.