The meaning of "heirloom"!

For many years I happily grew hybrid tomatoes. I understood the "hybrid" tomato was defined as a genetic cross between two "heirloom" tomatoes and the seed was reproduced commercially year after year after year.

At the same time, it was my understanding that an heirloom tomato was by definition a variety of tomato that had grown genetically true for at least 40 years.

Now we seem to have a class of tomatoes available that have wonderful qualities such as those produced by Brad Gates at Wild Boar Farms which have grown true for multiple generations but don't even come close to the forty year yard stick for heirlooms. I've noticed one commercial vendor who seems to come up with a different name for any tomato that shows a slight difference in his fields. He claims all kinds of wonderful virtues for his new tomatoes, but I question the validity of his claims. I've also noticed a number of vendors who carry fairly new varieties under the "heirloom" classification even if they really are not heirlooms.

Does a classification exist for the new varieties which seem to grow true through multiple generations but don't meet the "heirloom" standards?

Ted