Present perfect or past perfect in a (specific) sentence?

Question

I start with the assumption that the following sentence is correct.

John told me that his father had been ill since Christmas.

My question is whether the above sentence can also accommodate the present perfect, depending on the context.

John told me that his father has been ill since Christmas.

Here’s the context I believe would permit the present perfect. If the telling occurred very recently and it’s May, it means that John’s father has been ill for several months, and thus one can infer that he is still ill now, therefore the use of present perfect is appropriate.

[I saw John yesterday at the farmers’ market.] He told me that his father has been ill since Christmas.

Is my grammatical hunch (and its justification) correct? TIA

Answer 1

You are perfectly correct.

The past perfect could be used when reporting a conversation in an earlier year. At the time of speaking, the father had been ill; he may or may not have recovered since.

Answer 2

Your assumption is correct.

If it's May now and you saw John yesterday and he told you that his father had been ill since Christmas, which makes it a long-term illness, it's very unlikely for his father to have recovered since yesterday.

You are therefore perfectly justified in assuming John's father is still suffering from his long-term illness today and say:

I saw John yesterday at the farmers’ market. He told me that his father has been ill since Christmas.