Sounds pretty normal to me. There are a lot of little variables. One of them is that there might be a standard deviation for original capacity due to manufacturing variations.
Apple rates the battery at 500 complete charge-discharge cycles before a typical reduction in battery health to 80%. So if it's an average 250 cycles per year, a linear degradation would be expected to mean a reduction to 90% in one year. 99% doesn't sound like there's a problem.
Also - it's important to understand that the battery health number is just an estimate.