You only get a new set of vouchers when your new tracking period starts. The value of 'over-achieving' tier points comes from what AY calls milestone gifts. These are awarded as follows:
200k tier points = 40k bonus award points
300k tier points = 60k bonus award points
400k tier points = 100k bonus award points
And then there is of course Lumo at 450k tier points.
So 2 LH + 4 SH, right? How about 4 SH vouchers of reaching Gold, are they credited at all or also when new tracking period starts?