JR group has 7 companies; JR Hokkaido, JR East, JR Central, JR West, JR Shikoku, JR Kyushu and JR Freight. Except Shikoku and Freight, all 5 companies are operating Shinkansen.
Although it leaves from Tokyo station which Yamanote loop line is operated by JR East, Tokaido Shinkansen(Tokyo - Shin-Osaka) is operated by JR Central. Which means there are two stationmasters at Tokyo stations. Then, each Shinkansen has their own trains, which means Shinkansen trains of JR East will not run on Tokaido shinkansen.
JR East operates five Shinkansen. Tohoku, Akita, Yamagata, Joetsu and Hokuriku shinkansen. Then, due to compositions of the trains are different among the Shinkansen, not the same series of trains will run even on same tracks.
Hokuriku shinkansen is the newest Shinkansen for JR East, which connects Tokyo and Kanazawa. However, the operation to Kanazawa did not start at the beginning and the line was connecting Tokyo and Nagano due to winter Olympic games in Nagano in 1998. Till the extension to Kanazawa, though the Shinkansen was officially named Hokuriku shinkansen but normally called as Nagano shinkansen.
Before the extension, travelers had to change at Echigo-Yuzawa station from Joetsu shinkansen to limited express Hakuta which runs semi-private sector Hokuestu kyuko line, which means Japan Rail Pass holders had to pay the supplement. Or if they did not want pay the supplement, they had to take Tokaido shinkansen to Maibara and change to limited express Shirasagi, which takes longer than via Echigo-Yuzawa.
Therefore thanks to Hokuriku shinkansen, Japan Rail Pass holders can now easily reach Kanazawa or Toyama, the gateway for famous Tateyama Kurobe Alpen route.