Hi James and Jack
Has Jack already been tested for FIV? I take from your post that he may of had an in-house test, which can be a false pos sometimes you know, there is a percentage, others may know.
Anyways would just like to say, if Jack is not badly ill with FIV, he could have many more years to come if managed properly. Some members here have FIV cats which are well into their teens.
I also have a cat with mouth problems, its a severe gingivitis, he has had most of his teeth removed, although he does not have FIV. So hopefully Jack does not have FIV but going on what I hear here, FIV is really nothing to worry about