To be accurate, if the per serving carb amount is below .5 (from 0 to .49)per serving, manufacturers can put 0 carbs on their product. Anything between .5 and .99 can be expressed either as <1 carb or 1 carb, whichever they want to do.
Basically, they round down if less than half a carb and up if more than half a carb, so if something says zero carbs it will have anything from actual zero carbs up to just a hair under half a carb per serving.
When I am counting, unless it is meat, if something says 0 carbs, I estimate .25 carbs per serving and figure all together that will average the zero carb things I eat out about right.
"You have a masterpiece inside you, you know.
One unlike any that has ever been created, or ever will be.
If you go to your grave without painting your masterpiece, it will not get painted. No one else can paint it. Only you." ~~ Gordon MacKenzie