For people who are interested in Hadith topic.

Well, they didn’t feel the importance to collect and compile all the sahifas because everything was quite fresh in their memory, ao they concentrated more on putting ahadith in their actions, but the sahifas of ahadith were passed down from Sahaba like Abu Hurayra(ra), Ibn Abbas(ra) and Ibn Masud(ra) to the Successors.

Dr Jonathan writes in his book “Hadith(Muhammad’s Legacy in the Medieval and Modern world) " Some of the early Isnad that appear most regularly in Hadith collection seem to be a record of* Sahifas* being handed down from teacher to student or from father to son. We thus often find the Sahifa-isnad of Aby Hurayra to Abd al-Rahman, to his son al-Ala. The successor Abu al-Zubayr al-Makki received the sahifa of the companion Jabir b. Abdallah, and one of the most famous Successor, al-Hassan al-Basri(d.110/728), received the sahifa of the Companion Samura b. Jundub. An example of a sahifa that has survived intact today, the *sahifa *of the Successor Hammam b. Munabbih(d.130/747), contains 138 hadiths from the Prophet via Abu Hurayra.”

Also , you don’t find many ahadith narrated by khilafa rashidun but by the companions who were young and were for a shorter time with the Prophet, like Abu Hurayra(ra) who was only for 3 years with the Prophet(SAW) is the largest source for hadith, he didn’t have the ahadith written down then but he compiled all these ahadith later in his life, and Ibn Abbas(ra) who was only 14 years old when the Prophet(SAW) died, has compiled around 1,7000 ahadith. On the other side Abi Bakr(ra) is the source for only 142, Ali (ra) for 536 and Umer(ra) for 537.

Regarding the authenticity of a hadith, there’s ilm al-hadith and through this you can learn about the chain of a hadith and then there are other measures to knoe if a hadith is reliable or not, a hadith scholar can tell you all this.