The rule is clear. If your flight leaves from a B gate you don't get a limo (unless it's a B bus gate). If your flight leaves from C or Z you will get a limo. You don't get a limo if you are leaving for a Schengen destination.

Or as lufthansa.com tells you: "The limousine service to your aircraft is also available to you if you are using our First Class Lounge in Pier B at Frankfurt Airport. This service is available for Lufthansa flights to non-Schengen and non-EU countries which take off from a non-gate position or from Departure Areas A or C."