well, it's actually kinda weird. As far as I can tell, they where never introduced in order.

It is also interesting to note, some older Accord and Prelude engines where also "E" series (ES, ET) and "B" series (BS, BT) so it is fair to say the E series also parented the early A and B series. The First letter is the series, while the second seems to represent the displacement (V=1.3, W=1.5, S=2.0, T=1.8). The old system was kinda neat.