Just go by what the listed ingredients are on the label. You won't get the exact same taste but you'll get something real close to it.
Also if you'd like to try a better tasting V8 juice try the DeiFratelli Vegetable Juice. I like it much better than the Campbell's anyday and does not give me that awful bloated feeling the V8 gives me after drinking it. It's not available everywhere but well worth it if it is available in your local store. And it's cheaper too! And believe it or not it is canned right near where Campbell's V8 juice is canned in Napoleon Ohio. DeiFratelli is less than 75 miles away in Northern Ohio. Years ago my first husband worked for Campbell's in Napoleon, Ohio. He was in the spice mixing department and mixed all the spices for the soups and the juices. V8 is still canned in Napoleon.
You could try your own version of V8 as well. Remember they also add secret seasonings to the juice to give it a different flavor. You're not going to find the formula for that online. Sorry! Campbell's would have a hissy fit!
Thanks, Linda (?). Maybe someone does have a family recipe they would share with us.
The ingredients are listed, but no ratios, and I suspect that is the key, and as you said added spices.