There are a couple of points:

1. Most people are not too interested in the altitude and speed of an aircraft - just where it is on the map

2. It should be possible even with incomplete data to see if the data that has been uploaded by a single station is credible - is the position reported reasonable for the aircraft (by make and model, flying at that altitude) compared to prior positions reported. A B752 at 5000ft is only likely to be within - say - 10km of the position it was in 10s ago type thing.

The maths would be a pain to work out but if doing Pythagoras and you're only interested the approximate magnitude of the answer - don't do the square root calculation (divide lots of compute) square the other side of the calculation instead (multiply is faster). or even easier just have a lookup table. Its a (B75,b73, a32, a33, a34, etc) 10s since last position - whats the square of the maximum distance it could have travelled ... is the position given within that range?