One would think that an "heirloom" would stay within a family. I think I'd prefer just "open pollinated" for these widely circulating tomato varieties. But, like Farmerlon, I'm not willing to argue about it
Heirloom has more of a romantic sound to it and I'm sure, is appreciated by the catalog outfits. I have seen the Legend variety sold as an heirloom. It is open pollinated and certainly has the name but Legend is a Dr. James Baggett introduction and I think it came out about the time he retired in the late 1990's. Dr. Baggett has a lot of history but that tomato, not so much.
Some of the "heirloom" varieties that come to us from other countries were commercial varieties there. A tourist thought they were just wonderful and caught a flight home with some seed stuck to the front of his shirt. Nothing wrong with that.
An "heirloom" that grows well in my garden, Thessaloniki, seems to have been a Greek commercial variety brought here during the 1950's to be grown on American farms, if I got the information on it right. I was around during those days and don't remember anything about people trying to grow something special from grandma. We all seemed to be interested in the new and modern. And, I suppose that there were good reasons to allow some things just to fall by the wayside.
Now, what was new and modern 50 years ago, might be considered an antique or an heirloom. One thing, I think no one would want to lose what is truly good!