What Does My Birthday Mean

The birth date is used to calculate the numerology life path and all cycles in the numerology chart.

The birth day, the day of the month of the birth date, is used to calculate the first life period cycle and the first, third, and fourth pinnacle cycles.

Thus, it is significant for those calculations.

The number 11 would have extra significance as a master number if any of your core numbers were also a master number. But that's not the case with your numerology chart.

The Master Number Search article talks about master numbers and how they're determined.

I'm uncertain what you meant to ask when mentioning a chance of having a birthday the day before yours, because, of course, there's always that chance. If you were wanting assurance that the person you're thinking of is a twin flame, numerology doesn't have calculations to determine that. You can always use the marriage compatibility calculator to see if you are compatible for the long term. But compatibility doesn't guarantee or even imply twin-flame status.