Protein synthesis/ wobble hypothesis/ codons?

with the wobble hypothesis, can basically ingonre the last nucleotide. Only the first two matters, so many nucleotides?? well there are 4 different in the (RNA) nucleotides (G-C-A-U). and if only two them matter, then how many combinations can you get with just two nucleotides. 4^2 = 4*4 = 16 combinations. But wait a minutes, theres 20 diff. amino acids. Well some amino acids require all three nucleotides to be specific in order to be matched with their codon. This how the woblle can explain the deviations that occurs even if the last nucleotide in many cases is not important as the first two codons.