thats probably the best explination.
a = old blocks for the accord and the prelude
b = newer low displacement blocks
d = low displacement blocks from 20 years ago to current d17s in civics
f = accord/s2k blocks (the variant at the end tells you which).
h = prelude/euro accord high displacement blocks
k = current generation mid to high displacement blocks
l = current fit engine series.
e.g a b16a = a low (1.6L) displacement early revision engine (JDM Civics),
d15b = low displacement (1.5L) slightly older revision engine (JDM Civics),
h22a = high to mid displacement (2.2L) early revision (JDM Preludes).
F20C = mid displacement (2.0L) late revision (S2000).
The list goes on and on.