Hello Sydney! Welcome to the Disney Parks Moms Panel.
I'm sorry to hear that you have (as of yet) been unable to book Advanced Dining Reservations for
Cinderella's Royal Table. As a consummate "ball-dropper" myself, I've got your back.
The short answer to your question is that there are no guarantees that you will get those coveted
Advanced Dining Reservations, however, I have yet to be unable to get Advanced Dining Reservations for "must-try" Dining Locations when I've had enough time, patience, persistence, and flexibility.
With enough time, Advanced Dining Reservations often become available to Guests as the weeks and days get closer to your Magical Vacation. The difficult aspect of capitalizing is snapping up openings when they become available. It's not that Advanced Dining Reservations aren't consistently changing, it's about being the first one grabbing them on your My Disney Experience App or on the Dining Location Site Page before anyone else does.
I check My Disney Experience as many times as I can throughout the day. I am persistent to the point that I am confident that no one else will get the first cancellation that opens up.
The last element of getting those difficult Advanced Dining Reservations is flexibility. I rarely get the exact time (or even day) that I want for these Advanced Dining Reservations, however, tables often open up for times or dates "close to" my desired time and I book those immediately. I can always cancel said Advanced Dining Reservations if a better table opens up or if I change my mind.
For Cinderella's Royal Table, you will be returned the charge to your credit card for the meal with a cancelation of at least 24 hours.
Best of Luck!
~Todd