I know the source of Ran's October-birthday :
At the beginning of one of first Live Actions (Dorama), Shinichi had said Ran's birthday was on the previous day, and on class the blackboard wrote, October 2nd. So according to the Dorama her birthday is October 1st.
But I don't know how much influence Gosho has on the Dorama.
Plus it makes not much sense as Ran said her birthday is 'a way off' from Eri's (October 10th) like Wakarimashita wrote.
In Movie 1 Ran showed the horoscope of Taurus and said that her and Shinichi's lucky color this month is red.
I know that the Movies are Anime-Originals BUT Gosho has influence on them as he often talks in interviews about the ideas he had e.g. for the 15th or 16th movie.But I don't know if this detail was Gosho's idea,too.
Furthermore someone wanted to know Ran's blood type and I can say it's the same as Shinichi.(Volume 26)
Most people say blood type B but I don't know the source for it.
So they are same class,same blood type, maybe also same zodiac sign...
Perhaps Gosho wants to show in this way that Ran and Shinichi are soulmates.