Usually, a 470 k or 510 k resistor has a +/-5% tolerance, so the total range of both would go from 448 k to 535 k, well outside the 499 k +/- 1% band.
Include that in your calculation of the range of voltages to be expected from the converter.
As +/- 1% resistor values go, 499 k is quite popular: where have you looked for a replacement of the small part?