The long count calender does not rely on the type of accuracy you imagine, it marks the passage of time through celestial events and it is impossible for it to get off kilter.

Eclipses and planetary transitions of the Sun can be predicted using the Mayan system of time keeping within minutes of accuracy.

Though days are counted, no attempt is made to mark the length of a year in days other than the winter and summer solstices, which maked it impossible for the calender to get out of synchronicity with the true passage of an actual year. The Mayan calender does not require the constant readjustment of the Gregorian calender and is in fact much more accurate.