Background: This study aims to identify factors predicting recurrence and unfavorable prognosis in cN+ patients who have undergone sentinel lymph node biopsy (SLNB) following neoadjuvant chemotherapy (NAC). Methods: The retrospective multi-centre “MF18-02” and the prospective multi-centre cohort registry trial “MF18-03” (NCT04250129) included patients with cT1-4N1-3M0 with SLNB+/− axillary lymph node dissection (ALND) post-NAC. Results: A total of 2407 cN+ patients, who later achieved cN0 status after NAC and subsequently underwent SLNB, were studied. The majority had cT1-2 (79.1%) and N1 (80.7%). After a median follow-up time of 41 months, the rates of locoregional recurrence and axillary recurrence (AR) were 1.83% and 0.37%, respectively. No significant difference in locoregional recurrence or AR rates was observed between the SLNB/targeted axillary dissection-only (n = 1470) and ALND (n = 937) groups. Factors significantly linked with AR included age younger than 45 years, nonpathological complete response (non-pCR) in the breast, and nonluminal pathology. Locoregional recurrences were associated with nonluminal or HER2(+) pathology, non-pCR in the breast, and ALND. Poor prognostic factors for disease-free survival (DFS) included having cT3-T4, no breast pCR (non-pCR), ypN(+), and nonluminal pathology. No significant difference was found in DFS or disease-specific survival (DSS) rates among ypN0, ypN-isolated tumour cells, ypNmic, and ypN1. However, significant decreases in DFS and DSS rates were observed when comparing ypN2 or ypN3 disease with ypN0. Conclusions: The present large registry data indicate that younger patients (<45), those with nonluminal pathology, and those who only partially respond in the breast are more susceptible to axillary and locoregional recurrences.