In Part 1 of Tajweed Rules in English there is a chart detailing the chain of transmission for Hafs 'an Asim. At the level of the Companions, may Allah be pleased with them, some of them are mentioned more than once.

Question
Assalamu 'alaikum wa rahmatullahi wa barakatuh

I pray this reaches you in the best of iman and health, ameen.

My question is regarding sanad. In Part 1 of Tajweed Rules in English by Sister Kareema, jazahallahu khairan, there is a chart detailing the chain of transmission for Hafs 'an Asim. At the level of the Companions, may Allah be pleased with them, some of them are mentioned more than once.
How is this chart interpreted and meant to be understood?
Jazakallahu khairan
Wassalamu 'alaikum wa rahmatullahi wa barakatuh

Answer
Wa alaikum assalaam wa rahmatullahi wa barkaatuh
Al hamdu lillah we are well and blessed by Allah, may Allah reward you greatly and give you the best in this world and the Next. 
In the chart in the Tajweed Rules of the Qu'ran in English, when you see a block with a name and look at the names which fall above that, even if it is a portion of the block, you know that the reader or in this case the taabi' read to all of the Companions which the Taabi' block has a portion or all of his name below the upper block or blocks, may Allah be pleased with them.  To cover all the three  taabi'een in this sanad who read to the various Sahaba, the names had to be repeated over the other blocks of the taabi'een. 
So Abulrahman As-Sulamee read to five of the Companions (Abdullah bin Mas'ood, Ubayy bin Ka'b, Zayd bin Thaabit, 'Uthman bin 'Affan, and 'Ali bin Abi Taalib) , Zirr bin Hubaysh read to three Companions ('Ali bin Abi Taalib, 'Uthmaan bin 'Affan, and Abdullah bin Mas'ood), and Sa3d bin Iyaas Ash-Shaybanee, read to one Companion (Abdullah bin Mas'ood), .  May Allah be pleased with them all.
Wa iyyaakum
Wa alaikum assalaam wa rahmatullahi wa barakaatuh