Am I missing something? I hope that I am. After viewing several recipes on this site which use Grain proteins (including Soylent 1.4), I haven’t seen any which adjust for both the amino acid score (AAS) and protein digestibility (PD). Only one recipe which I’ve viewed, other than Soylent 1.4 adjusted for AAS but there was no adjustment for PD. Soylent 1.4 appears to adjust for AAS but I haven’t seen any mention of an adjustment for PD.
Most recipes use a complete protein as the primary protein source, so there’s no great need to adjust for the PDCAAS of the oats or other grain which are also in the mix.
Soylent uses a sprouted brown rice protein, which has a score of 1.0. My DIY, and many others, use whey, which has a score of 1.0
If you look at a popular DIY, like People Chow, it uses whey for 50 g of protein with a PDCAAS of 1.0, and the excess comes from the masa harina. The AAS profile of masa harina is lysine-limited. Whey, however, contains an excess of lysine, improving the net score of the blend. Oats are also lysine-limited, though not as much as masa harina.
Although this doesn’t fully take into account the question of the digestibility of the protein in the masa harina or the oat flour, you’re not in a range where you really need to worry about the margins, as long as your primary protein source is complete (or is a complete blend.)
At a minimum, I would suggest the DRI (2005) amino acid scoring pattern:
Methionine + cysteine (SAA), 25
Phenylalanine + tyrosine, 47
Multiply the total grams of protein in the recipe by each of the above. Your actual total for each amino acid in your recipe should exceed the scoring pattern. That ensures an adequate blended quality of protein.
This is why I, like a lot of people, use whey protein in my DIY.