That's certainly possible. There's a gap in any information about the dating of numbers Kosta used between about 1963 and 1986, at least as I've been able to find out. The algae vase you show was designed in 1963. That means between 1955, when Kosta started at 1000, and 1963, when 1784 was produced, 784 designs were created in the hand made category. 3054 is almost 1300 designs later, which is why I guessed it was designed pretty close to when the numbering system was changed in the 70's. But you're right, I'm only guessing and your estimation is just as valid.