Learn English – How to say date relative to an event in the past from present perspective

You use "the" when referring to a time period rather than a date

In the 1700s

In the 6th century

You should also use "the" in certain date formats.

Today is the 7th of September

without "of", the above does not work.

Today is September 7th

is also acceptable.

I don't think I've ever heard someone from the UK say "today is 7th september", despite the date format being dd/mm/yyyy.

In all three cases, the present perfect is appropriate because we're discussing potential events or conditions that occurred at or have continued from some point in the past right up to the present. Since the father is still alive and still employed, it's presumed that the suffering and employment condition continue to the present day.

The past perfect isn't appropriate in these three examples because we're not describing an event or condition that entirely occurred earlier than some other event. (And when we do, we do indeed use the past perfect: "...we had thought a holiday in Scotland would be relaxing for him." Here, the prediction that the holiday would be restorative took place before the illness and then ceased, having been falsified. Or "...we'd been trying to persuade him to have a break for ages before he agreed." The attempts at persuasion ended once he agreed.) Barring alleviation from stress, the person is still suffering; barring separation from his job, he is still working.

It is true that the length of time ("recently") is not explicitly defined. "Some time" could be anything from weeks to years. However, this vagueness doesn't change the fact that the inquiry addresses a period that began in the past and continues to the present day; the same can be said about the suffering and the working. Thus, the present perfect is the right choice.