Frank:
The varieties on the list were not selected for taste or productivity, just being VERY early to get a jump on the season, so that may be why they are unfamiliar to you. There are few "beefsteaks" on the list, I suspect because large tomatoes take more time to ripen. I don't know why no Roma-like paste tomatoes are very early (55 DTM or less). Very early tomatoes are often sought by people in cool or short season climates like northern Canada, but I know your Nova Scotia seasons are much like mine in Connecticut. (Many years ago on an eclipse expedition to Greenland, our plane was stranded in N.S. for several days, so I got so see some of your sights including the Marconi wireless station.)
Mighty Sweet Hybrid is a grape tomato, and some other early grapes that didn't make the list are Grape(62 days), Red Grape(60), Sugary(60-65), and a couple of others I couldn't find sources for.
Sungold (aka Sun Gold) is a very popular early tomato. Some sources list it as 55 DTM, but just as many say 60 or 65. I listened to the many grower reports on the web that said it was early, not very early, so it did not make this list (but I'm growing it anyway!)
@fwmosher
And as for your last question, many of the tomatoes on the list are hybrids (as is Sun Gold). I'm not predjudiced in favor of either hybrids or OP varieties.
Oh, and in case you are wondering, the varieties in bold face are the one's I am thinking of trying (not all at once) in the next few years. I just forgot to remove the bold face before taking a screen shot of the spreadsheet.