Common/Generator/DateNumberGenerator.php
protected function generateNumber($number)
    {
        $datePrefix = (new \DateTime())->format($this->prefix);

        if (0 !== strpos($number, $datePrefix)) {
            $number = 0;
        } else {
            $number = intval(substr($number, strlen($datePrefix)));
        }

        if ($this->debug && 9999 > $number) {
            $number = 9999;
        }

        return $datePrefix . str_pad($number + 1, $this->length - strlen($datePrefix), '0', STR_PAD_LEFT);
    }
protected function generateNumber($number)
    {
        $datePrefix = (new \DateTime())->format($this->prefix);

        if (0 !== strpos($number, $datePrefix)) {
            $number = 0;
        } else {
            $number = intval(substr($number, strlen($datePrefix)));
        }

        if ($this->debug && 9999 > $number) {
            $number = 9999;
        }

        return $datePrefix . str_pad($number + 1, $this->length - strlen($datePrefix), '0', STR_PAD_LEFT);
    }
Generates the number.

@param string $number

@return string