Layah, I'm not sure if you are overreacting, but perhaps you are frustrated because you haven't found information that backs up your theory.   

Beef has been "corned", not just for Lent, but also to preserve it for export.

As for "Jewish" corned beef, I still say that there is relatively no difference (besides the kosher process). One brand may add spices in a different order or amount, but the brining process is the same. You might have a company that markets corned beef toward a specific ethinic group, but the product is the same. The taste may be a bit different, just like a McDonalds hamburger tastes different from Burger Kings and both are radically different from what I can make at home. They are all hamburgers.

When I went to the supermarket last week, there were 3 or 4 brands of corned beef available. One or two said they were kosher, the others did not. None claimed to be either Irish or Jewish.

Because of the similarities, many people often confuse pastrami with corned beef.   Pastrami, which actually has origins in Turkey, is argueably more popular in Jewish deli's, at least here in the NYC area.