Inconsistencies in fermentable ppg calculation

[Vaat]

Hello,

I've been searching around the net and trying to figure out what is the correct formula, using a malt spec sheet, to calculate the ppg value that I can use when adding a Custom Fermentable in BF.

According to this article:

http://www.brewersfriend.com/2012/11/30 ... finitions/

.. I should basically account with moisture content (MC%) and extract fine grind value (DBFG%). However, this gives lower ppg values than is widely referenced for given grains. It feels as if all the other sources do not account for MC%..

For example, I have a spec sheet of Weyermann Pale Ale, where:
- Moisture content = 4% max
- Extract dry substance = 79% min

Using formula:
ppg = 0.46214 * DBFG * (1-MC) * 100
.. I calculate:
0.46214 * 77% * (1 - 4.5%) * 100 = 35.049

However, for the reference, there is an add-on feature in BeerSmith that allows to add custom malts and their Weyermann Pale Malt gives ppg as 38.

1) Does anybody know what is the really correct way to calculate the ppg?
2) I've seen all the malt specs give MC% as "max" and DBFG% as "min", but how can I know what is the range (maybe DBFG is in range of 79%..82%, which would make a big difference)?

Thanks!