Why not post some pictures? If it tastes good, I doubt it is white tomesol. Did you look through the other tomatoes offered by BC Heirlooms, does it match any of those? If it is a tasty hybrid, save some seeds and grow them out.

I grew White Tomesol 4 years ago with seeds from BC. I gave away 4-5 seedlings to people where my DW works. I got 2 tom's that tasted so so, like most everythng else that I grew that year. 2 tom's were sent home with the wife from a gal that grew them 20 miles away. Slightly yellow and about 8 oz. (not like the picture in BC's catalog..PURE white)
I too was very surprised at how great they tasted. I gave seeds to the grower and she has grown them every year since. It's her favorite tomato.

Thanks for the responses. Sorry about not having pix; tech-phobic, old guy syndrome. This is really a nondescript, small yellow beefsteak. Nothing about its appearance suggests something special. Quite the opposite. BC has one variety, Golden Monarch, that sounds somewhat similar (if you can really compare verbal descriptions), but not the same. I've emailed BC heirlooms but haven't heard back yet. I, like many folks out there I'm sure, have become quite adept at looking for certain buzzwords in the descriptions to give me clues about taste. What else can we do? I'm definitely going to grow this out and see if it repeats, stabilize if possible. Thanks, and happy gardening.

Well hopefully you have a lucky mistake. Two of my best tasting tomatoes were stray seeds. Actually, both came from a packet of Black Krim seeds (one purchased from one supplier a few years ago, another from a different black krim packet purchased from another supplier last year). I have named them 'red (or pink) krim', and 'brown krim'. Seeds from Red Krim have produced extremely well in the last 2 years. This is the first year growing Brown Krim, from last year's seed mistake, hopefully they are as similar to the parent as the Red Krim's were.