The Request TV shows page clearly states that Netflix keeps tracks of all requests from subscribers, so there’s no need to request a certain project more than the first time.
The “Request TV shows or movies” page can be accessed here or by going to the help center in your Netflix account.
Content can’t make its way to Netflix if the rights are exclusive to another company, the streaming rights are not available to purchase from the content provider, and other variables like popularity, cost, availability, and localized factors.