Adding rice might get you close to that for the amount of rice you eat, but 1 cup of beans will get you 16g of protein and 1 cup of rice will get you 4g of protein.
So a chunk of your protein intake would still be incomplete. It's not like the ratios are perfect so that a cup of each gets you 20g of PDCAAS 1.0 protein. Doing some quick napkin math looking at the AA makeup and protein digestibility of the two, it's like 14g equivalent of PDCAAS 1.0 protein.
~25% is a pretty significant gap if you're trying to hit optimal levels for things like muscle growth, etc.
From what you just wrote, it appears you misunderstood what I said. Just to be clear:
Red kidney beans (50g): PDCAAS = 0.88, Protein = 11.25g
Basmati rice (50g): PDCAAS = 0.7, Protein = 4.5g
Red beans + rice (50g, 50g): PDCAAS = 1.0, Protein = 15.75g
Milk (500g..): PDCAAS = 1.0, Protein = 15.5g
So, from a protein perspective (according to PDCAAS), 500g of milk will give you the same amount of usable protein as the 100g rice and beans meal. There is nothing left on the table.
So, just eating kidney beans, PDCAAS would say that you aren't really getting the full benefit of the "protein on the label". But once you combine it with rice, you are getting the full benefit (according to PDCAAS).
You can't look at the digestibility of the two foods in isolation to make the calculations.
As long as you are eating a varied diet, PDCAAS is pretty pointless. If you have an eating disorder, or food scarcity issues, then it might become important.
So a chunk of your protein intake would still be incomplete. It's not like the ratios are perfect so that a cup of each gets you 20g of PDCAAS 1.0 protein. Doing some quick napkin math looking at the AA makeup and protein digestibility of the two, it's like 14g equivalent of PDCAAS 1.0 protein.
~25% is a pretty significant gap if you're trying to hit optimal levels for things like muscle growth, etc.