Immune deficits after CD19 chimeric antigen receptor (CAR) T-cell therapy can be long-lasting, predisposing patients to infections and non-relapse mortality. In B-cell non-Hodgkin lymphoma (B-NHL), the prognostic impact of immune reconstitution (IR) remains ill-defined, and detailed cross-product comparisons have not been performed to date. In this retrospective observational study, we longitudinally characterized lymphocyte subsets and immunoglobulin levels in 105 B-NHL patients to assess patterns of immune recovery arising after CD19 CAR-T. Three key IR criteria were defined as CD4⁺ T helper (T_H) cells > 200/µL, any detectable B cells, and serum immunoglobulin G (IgG) levels >4 g/L. After a median follow-up of 24.6 months, 38% of patients displayed T_H cells, 11% showed any B cells, and 41% had IgG recovery. Notable product-specific differences emerged, including deeper T_H cell aplasia with CD28z- versus longer B-cell aplasia with 41BBz-based products. Patients with any IR recovery experienced extended progression-free survival (PFS) (median 20.8 vs. 1.7 months, p < 0.0001) and overall survival (OS) (34.9 vs. 4.0 months, p < 0.0001). While landmark analysis at 90 days confirmed improved PFS in patients with any recovery (34.9 vs. 8.6 months, p = 0.005), no significant OS difference was noted. Notably, 72% of patients with refractory disease never displayed recovery of any IR criteria. Early progressors showed diminished IR at the time of progression/relapse compared to patients with late progression/recurrence (after Day 90). Our results highlight the profound immune deficits observed after CD19 CAR-T and shed light on the intersection of IR and efficacy in B-NHL. Importantly, IR was impaired considerably postprogression, carrying significant implications for subsequent T-cell-engaging therapies and treatment sequencing.