Obviously we need to add the date the coordinates were encoded. The decoding will have to apply correction based on ample databases of tectonic data. A simple formula will not work, a major earthquake can move a rift by some 5-10 cm. And you need to know exactly what plate does the coordinate refer to, is not as simple as 'Australia moves 7cm a year', consider parts of California east vs. west of the fault. Well, that spiraled out of control fast... It makes the time issues like [0] seem trivial by comparison.

[0] http://stackoverflow.com/questions/6841333/why-is-subtractin...