DIYbanter - # Bricks In English Garden Wall Bond?

I'm computing various types of masonry bonds & the # of bricks & amount of mortar consumed in each type. I'm a bit stuck on English Garden Wall Bond at the moment & hopefully someone can confirm my methodology (I know 1/2 Thick Garden Wall Bond is rare but this is for exercise purposes):

- Spons 1st Stage Estimating 2nd Edition says for a 1/2 thick Garden Wall Bond - 74 Bricks;

- http://www.fatbadgers.co.uk/Britain/Brick%20Bonding.htm says 72 Bricks;

My manual calcs says 66.6666 bricks; I know it'd be rounded up but I'm working to 4 decimal places for the purposes of thousands of m2 it'll be more accurate. Please disregard waste factors here; we're interested in nett quantities at the moment. So here's my calcs; hopefully someone can confirm I'm right or point out where I'm going wrong:

English Garden Wall Bond - 1 course of headers : 3 courses stretchers:

Headers:
1m h / 0.075 = 13.3333 # courses overall (inc'd headers);

13.3333 # courses overall / 4 courses every header row consumed = 3.3333 header courses;

1m l / 0.075 = 13.3333 bricks each header row;

13.3333 * 3.3333 = 44.4439 bricks total for all header rows if it was a 1 thick wall; but this is half thick wall so / 2:
44.4439 / 2 = 22.2220 # bricks.

Stretchers:
13.3333 # courses overall - 3.3333 stretcher courses = 10 stretcher rows;

1m l / 0.225 = 4.4444 # bricks in each stretcher row;

10 stretcher rows * 4.4444 # bricks in each stretcher row = 44.444 # bricks in all stretcher rows.

Totals:
22.222 # bricks in header rows + 44.444 # bricks in stretcher rows = 66.666 bricks per m2.