Actually, I'd lower my actual WR to be less than the calculated SWR. But I see your point and it's a good one. If your budget, driven by some of your spending categories rising faster than CPI, rises faster than inflation, your annual CPI increases will not keep up.
Whether CPI = your personal rate of inflation or not is certainly a big risk in determing FIRE status. And, as you say, medical care is an area where this could certainly happen. There are others, such as food and energy, also being pointed out.