They have six digit numbers in the 9xxxxx sequence, though, so they are presumably centrally logged somewhere and as some of the more recently delivered conventional track machines also have numbers like this ( e.g. 928001 ), I suspect they're registered in a single track machinery listing.
Partial listing below, but it's very, very incomplete - there are far more of these things than are shown here:
904083
910005
910006
910015
910023
910029
910030
910031
910032
910038
910040
910052
910054
910055
910056
910062
910069
910088
910098
910109
910144
910159
910194
911006
911009
911011
911012
911016
911018
911043
911044
911064
911100
911104
911106
911107
911137
911139
911142
911143
911144
911149
911153
911175
911207
911249
911252
911258
911272
911273
911285
911292
911307
911351
911619
912013
912089
912095
912096
912098
912104
912116
912121
912127
912138
912149
912152
912158
912182
912214
912221
912224
912237
912293
912296
912311
912312
912315
912338
912339
912340
912342
912351
912381
912384
912409
912414
912415
912420
912473
912485
912522
912523
914002
914048
914061
914098
914106
917003
919021
919022
919024
940002
940017
940018
940025
940031
940046
940048
940049
940051
940060
940061
940075
940078
940081
940082
940113
940115
940116
940121
940122
940124
940134
940135
940144
940147
940148
940163
940183
940189
940198
940203
940216
940240
940291
940292
940325
940329
940331
940336
940356
940526
940584
940633
940669
940691
940700
940711
940712
940733
940734
940738
940758
940763
940777
940779
940815
940893
940909
940913
940945
940971
940972
940974
941040
941044
941052
941091
941104
941107
942008
942012
942021
942034
942052
942054
942064
942069
942070
942098
942100
942156
942157
943044
944003
949007
966098
970003
970033
970063
970073
970080
970081
977013
979046