Duplicate stations across datasets R2, R6, and R7:
20049:
  R2:  [57.97, 81.80, 1891-1999, "Rudolf island"]
  R7:  [57.97, 81.80, 1941-1990, "OSTROV RUDOLFA"]
20087:
  R2:  [91.13, 79.50, 1891-1999, "Domaschniy island (Golomyannyi)"]
  R7:  [90.62, 79.55, 1954-1990, "MYS GOLOMYANNYY"]
20274:
  R2:  [82.23, 77.50, 1891-1999, "Uyedineniya island"]
  R7:  [82.23, 77.50, 1940-1990, "OSTROV UEDINENIYA"]
20292:
  R2:  [104.28, 77.72, 1891-1999, "Cheluskin,AMSG (im. E.K.Fedorova)"]
  R7:  [104.30, 77.72, 1940-1990, "MYS CHELUSKIN"]
20667:
  R2:  [70.03, 73.33, 1891-1999, "Bely island"]
  R7:  [70.05, 73.33, 1940-1990, "OSTROV BELYY"]
20674:
  R2:  [80.23, 73.50, 1891-1999, "Dixon island"]
  R7:  [80.23, 73.50, 1940-1990, "OSTROV DIKSON"]
20744:
  R2:  [52.73, 72.38, 1891-1999, "Maliye Karmakuly"]
  R7:  [52.73, 72.38, 1940-1990, "MALYE KARMAKULY"]
20864:
  R6:  [   71.83,  71.50, 1961-2000, " tambey"]
  R7:  [71.82, 71.48, 1940-1990, "TAMBEY"]
20891:
  R2:  [102.47, 71.98, 1891-1999, "Khatanga"]
  R7:  [102.47, 71.97, 1940-1990, "KHATANGA"]
20963:
  R6:  [   78.47,  70.88, 1961-2000, " gyda"]
  R7:  [78.45, 70.88, 1940-1990, "GYDA"]
20967:
  R6:  [   72.60,  70.22, 1961-2000, " seyakha"]
  R7:  [72.52, 70.15, 1936-1990, "SEYAKHA"]
21432:
  R2:  [137.90, 76.00, 1891-1999, "Kotelny island"]
  R7:  [137.90, 76.00, 1940-1990, "OSTROV KOTELNYY"]
21636:
  R2:  [139.88, 73.35, 1891-1999, "Kigilyakh cape"]
  R7:  [139.88, 73.35, 1940-1983, "KIGILYAKH"]
21647:
  R2:  [143.23, 73.18, 1891-1999, "Shalaurova island"]
  R7:  [143.93, 73.18, 1940-1990, "MYS SHALAUROVA"]
21824:
  R2:  [128.92, 71.58, 1891-1999, "Tiksi"]
  R7:  [128.92, 71.58, 1940-1990, "BUKHTA TIKSI"]
21921:
  R2:  [127.40, 70.68, 1891-1999, "Kyusyur"]
  R6:  [  127.40,  70.68, 1961-2000, " kjusjur"]
21931:
  R2:  [136.22, 70.75, 1891-1999, "Kazach'ye (Yubileinaya)"]
  R7:  [136.22, 70.75, 1965-1990, "KAZACHIE"]
21946:
  R6:  [  147.88,  70.62, 1961-2000, " chokurdah"]
  R7:  [147.88, 70.62, 1945-1990, "CHOKURDAH"]
21965:
  R2:  [162.40, 70.63, 1891-1999, "Chetyrekhstolbovoy isl."]
  R7:  [162.40, 70.63, 1940-1990, "O.CHETYREKHSTOLBOY"]
21982:
  R2:  [178.53, 70.97, 1891-1999, "Vrangelya island"]
  R7:  [181.52, 70.97, 1940-1990, "OSTROV VRANGELYA"]
22165:
  R2:  [43.30, 68.65, 1891-1999, "Kanin Nos"]
  R6:  [   43.30,  68.65, 1961-2000, " kanin_nos"]
22235:
  R2:  [37.03, 67.37, 1891-1999, "Krasnoshelye"]
  R6:  [   37.03,  67.37, 1961-2000, " krasnoscele"]
22292:
  R2:  [48.77, 67.70, 1891-1999, "Indiga"]
  R6:  [   48.77,  67.70, 1961-2000, " indiga"]
22471:
  R2:  [44.22, 65.87, 1891-1999, "Mezen'"]
  R6:  [   44.22,  65.87, 1961-2000, " mezen"]
22845:
  R2:  [38.93, 61.50, 1891-1999, "Kargopol"]
  R6:  [   38.93,  61.50, 1961-2000, " kargopol"]
23022:
  R2:  [60.75, 69.82, 1891-1999, "Yugorskiy Shar (post)"]
  R7:  [61.68, 69.77, 1940-1990, "AMDERMA"]
23024:
  R6:  [   60.42,  69.65, 1961-2000, " belyy_nos"]
  R7:  [60.33, 69.48, 1943-1990, "BELYY NOS"]
23032:
  R2:  [66.82, 69.72, 1891-1999, "Marre-sale"]
  R7:  [66.80, 69.72, 1940-1990, "MARRE-SALE"]
23074:
  R2:  [86.17, 69.40, 1891-1999, "Dudinka,AMSG"]
  R6:  [   86.17,  69.40, 1961-2000, " dudinka"]
23242:
  R2:  [72.95, 67.70, 1891-1999, "Novy-Port"]
  R6:  [   72.90,  67.70, 1961-2000, " novyy_port"]
  R7:  [72.92, 67.68, 1975-1990, "NOVYY PORT"]
23274:
  R2:  [86.57, 67.47, 1891-1999, "Igarka,AMSG"]
  R6:  [   86.57,  67.47, 1961-2000, " igarka"]
23330:
  R2:  [66.53, 66.53, 1891-1999, "Salekhard"]
  R6:  [   66.53,  66.53, 1961-2000, " salekhard"]
23383:
  R2:  [93.47, 66.88, 1891-1999, "Agata"]
  R6:  [   93.47,  66.88, 1961-2000, " agata"]
23405:
  R2:  [52.17, 65.45, 1891-1999, "Ust-Tsilma"]
  R6:  [   52.27,  65.45, 1961-2000, " ust_cilma"]
23552:
  R2:  [77.82, 64.92, 1891-1999, "Tarko-sale"]
  R6:  [   77.82,  64.92, 1961-2000, " tarko_sale"]
23678:
  R2:  [87.95, 63.15, 1891-1999, "Verkhne-Imbatsk"]
  R6:  [   87.95,  63.15, 1961-2000, " verhne_imbatskoe"]
24105:
  R2:  [102.37, 68.47, 1891-1999, "Yessey"]
  R6:  [  102.17,  68.47, 1961-2000, " essej"]
24143:
  R2:  [124.00, 68.73, 1891-1999, "Dzhardzhan"]
  R6:  [  124.00,  68.73, 1961-2000, " dzhardzhan"]
24329:
  R2:  [114.28, 66.25, 1891-1999, "Shelagontsy"]
  R6:  [  114.28,  66.25, 1961-2000, " selagoncy"]
24382:
  R2:  [143.23, 66.45, 1891-1999, "Ust'-Moma"]
  R6:  [  143.23,  66.45, 1961-2000, " ust_moma"]
24671:
  R2:  [135.87, 63.95, 1891-1999, "Tompo"]
  R6:  [  135.87,  63.95, 1961-2000, " tompo"]
25173:
  R2:  [180.52, 68.92, 1891-1999, "Schmidta, cape"]
  R7:  [180.53, 68.92, 1940-1986, "MYS SCHMIDTA"]
25248:
  R2:  [168.23, 67.33, 1891-1999, "Ilirney"]
  R6:  [  168.23,  67.33, 1961-2000, " ilirneyj"]
25325:
  R2:  [159.42, 66.55, 1891-1999, "Ust'-Oloy"]
  R6:  [  159.42,  66.55, 1961-2000, " ust_oloy"]
25378:
  R2:  [180.88, 66.35, 1891-1999, "Kresta, bay (Egvekinot)"]
  R6:  [  180.88,  66.35, 1961-2000, " egvekinot"]
25392:
  R2:  [188.07, 66.97, 1891-1999, "Serdtse-Kamen'"]
  R7:  [188.17, 66.93, 1943-1990, "CAPE NETTEN"]
25399:
  R2:  [190.17, 66.17, 1891-1999, "Uelen"]
  R7:  [190.17, 66.17, 1940-1990, "MYS UELEN"]
25400:
  R2:  [150.90, 65.73, 1891-1999, "Zyryanka,AMSG"]
  R6:  [  150.90,  65.73, 1961-2000, " zyryanka"]
25538:
  R2:  [164.23, 64.22, 1891-1999, "Verkhne-Penzhino"]
  R6:  [  164.58,  64.13, 1961-2000, " verhnee_penzino"]
25594:
  R2:  [186.77, 64.43, 1891-1999, "Provideniya Bay"]
  R7:  [186.77, 64.42, 1940-1987, "BUKHTA PROVIDENIYA"]
25705:
  R2:  [152.32, 62.45, 1891-1999, "Srednekan"]
  R6:  [  152.32,  62.45, 1961-2000, " srednekan"]
26063:
  R2:  [30.30, 59.97, 1891-1999, "Leningrad"]
  R6:  [   30.30,  59.97, 1961-2000, " leningrad"]
34561:
  R2:  [44.45, 48.67, 1891-1999, "Volshskiy GMO"]
  R2:  [44.45, 48.67, 1891-1999, "Volgograd,SKhI"]
35188:
  R2:  [71.37, 51.13, 1891-1999, "Tselinograd,GMO"]
  R2:  [71.37, 51.13, 1891-1999, "Tselinograd"]
35700:
  R2:  [51.85, 47.02, 1891-1999, "Gur'ev,AS"]
  R2:  [51.85, 47.02, 1891-1999, "Gur'ev"]
36003:
  R2:  [76.95, 52.28, 1891-1999, "Pavlodar,AS"]
  R2:  [76.95, 52.28, 1891-1999, "Pavlodar"]
38836:
  R2:  [68.80, 38.55, 1891-1999, "Dushanbe,AGRO"]
  R2:  [68.78, 38.58, 1891-1999, "Dushanbe,GMO (closed)"]
Number of dupes in each dataset combination:
  R2R2:   5 (34561 35188 35700 36003 38836 )
  R2R6:   25 (21921 22165 22235 22292 22471 22845 23074 23274 23330 23383 23405 23552 23678 24105 24143 24329 24382 24671 25248 25325 25378 25400 25538 25705 26063 )
  R2R6R7:   1 (23242 )
  R2R7:   21 (20049 20087 20274 20292 20667 20674 20744 20891 21432 21636 21647 21824 21931 21965 21982 23022 23032 25173 25392 25399 25594 )
  R6R7:   5 (20864 20963 20967 21946 23024 )
Station numbers in list-52_stn_numbers.txt that are not in non_c_station_list.txt:
  25121
  25123
  25151
Station numbers in list_51_stn_numbers.txt that are not in non_c_station_list.txt: