Bopearachchi does not account for the dating of Plato's coins in his encyclopaedia and accordingly gives Antimachus II a later reign. This is a rare lapsus in his very extensive work, but a lapsus it is: he simply interprets the dating as an additional monogram without further discussion. 

 A description of a monogram of Plato is found here: http://www.snible.org/coins/hn/bactria.html (though the coin referred to there is from 166 BCE). 

 The article on the tax-receipt is published after Bopearachchi's work and strongly indicateds that Antimachus II was the son of Antimachus I. Therefore, a close succession is very logical, and thus the altered reign 172-167 (keeping the estimate of five years done by Bopearachchi).