لماذا يظهر إختلاف في عمود Non-Null Count مش كلهم 28800 ؟

السلام عليكم

عند استخدم الكود ده 

ده الكود 

print(data_train.info())

ودي النتجيه 

#   Column                  Non-Null Count  Dtype
---  ------                  --------------  -----
 0   ID                      28800 non-null  int64
 1   dri_score               28374 non-null  object
 2   psych_disturb           26592 non-null  object
 3   cyto_score              18832 non-null  object
 4   diabetes                26540 non-null  object
 5   hla_match_c_high        24180 non-null  float64
 6   hla_high_res_8          22971 non-null  float64
 7   tbi_status              28800 non-null  object
 8   arrhythmia              26480 non-null  object
 9   hla_low_res_6           25530 non-null  float64
 10  graft_type              28800 non-null  object
 11  vent_hist               28541 non-null  object
 12  renal_issue             26748 non-null  object
 13  pulm_severe             26485 non-null  object
 14  prim_disease_hct        28800 non-null  object
 15  hla_high_res_6          23516 non-null  float64
 16  cmv_status              28166 non-null  object
 17  hla_high_res_10         21637 non-null  float64
 18  hla_match_dqb1_high     23601 non-null  float64
 19  tce_imm_match           17667 non-null  object
 20  hla_nmdp_6              24603 non-null  float64
 21  hla_match_c_low         26000 non-null  float64
 22  rituximab               26652 non-null  object
 23  hla_match_drb1_low      26157 non-null  float64
 24  hla_match_dqb1_low      24606 non-null  float64
 25  prod_type               28800 non-null  object
 26  cyto_score_detail       15689 non-null  object
 27  conditioning_intensity  23489 non-null  object
 28  ethnicity               28213 non-null  object
 29  year_hct                28800 non-null  int64
 30  obesity                 26923 non-null  object
 31  mrd_hct                 12203 non-null  object
 32  in_vivo_tcd             28575 non-null  object
 33  tce_match               9804 non-null   object
 34  hla_match_a_high        24499 non-null  float64
 35  hepatic_severe          26719 non-null  object
 36  donor_age               26992 non-null  float64
 37  prior_tumor             26837 non-null  object
 38  hla_match_b_low         26235 non-null  float64
 39  peptic_ulcer            26215 non-null  object
 40  age_at_hct              28800 non-null  float64
 41  hla_match_a_low         26410 non-null  float64
 42  gvhd_proph              28575 non-null  object
 43  rheum_issue             26472 non-null  object
 44  sex_match               28539 non-null  object
 45  hla_match_b_high        24712 non-null  float64
 46  race_group              28800 non-null  object
 47  comorbidity_score       28323 non-null  float64
 48  karnofsky_score         27930 non-null  float64
 49  hepatic_mild            26743 non-null  object
 50  tce_div_match           17404 non-null  object
 51  donor_related           28642 non-null  object
 52  melphalan_dose          27395 non-null  object
 53  hla_low_res_8           25147 non-null  float64
 54  cardiac                 26111 non-null  object
 55  hla_match_drb1_high     25448 non-null  float64
 56  pulm_moderate           26587 non-null  object
 57  hla_low_res_10          23736 non-null  float64
 58  efs                     28800 non-null  float64
 59  efs_time                28800 non-null  float64