When did soy become complete?

As in complete protein. I noticed a local health food store advertising that soy is a complete protein. Looking on the web I find the same. I was under the impression plant proteins are not. What is the SD?

From The Tufts University Guide to Total Nutrition:

Unless you are gluten intolerant, it is extremely likely in U.S. culture, vegetarian or not, that you will regularly take in sufficient products made of wheat so that the soy will be both complete and in full amounts. But it is stretching the meaning of the term complete by a bit.

Soybeans have always been a good protein source. You may be thinking of corn, which is normally low in the essential amino acid lysine. However, high lysine corn is now available.