Regarding the ambiguity in the martyrdom date of Lady Fatima, Islamic scholars have mentioned different causes. Some maintain that the ambiguity originates from a misunderstanding caused by the way scribes registered the martyrdom date of Fatima.
There are many historical facts which are buried in their time and never came to be known by the following generations. Behind important historical secrets, there might be significant political reasons that caused them ended up in graves with the people who kept them in their hearts.
Regarding the ambiguity in the martyrdom date of Lady Fatima, Islamic scholars have mentioned different causes. Some maintain that the ambiguity originates from a misunderstanding caused by the way scribes registered the martyrdom date of Lady Fatima (as). Early Arabic writing included no dots. The dots found today in Arabic writing were one of the first innovations that came after the spread of Arabic (after Islam). These dots make it clear how the letter should be pronounced. Before the dots, people read the text without any dots. Years after the Lady Fatima's departure, the scribes registered the date with no dots. Therefore, the phrase (خمس وسبعون) 75 days after the death of Prophet Muhammad (pbuh&hf) could also be read (خمس و تسعون) 95 days after the death of Prophet Muhammad (pbuh&hf) with a replacement of dots on letters.
Moreover, many sources indicate that during Umar's reign as Muslims Caliph, he banned all forms of hadith including writing, reporting or transmission. He clearly stated that the book of Allah would suffice Muslims. The ban on hadith was not lifted until the period of Umar ibn Abd al-Aziz. The prohibition of writing hadith kept people away from writing related subjects to the household of the Prophet (pbuh&hf). Furthermore, as a result of the remnants of the Arabic culture from the days of ignorance, very little attention was paied to issues related to females including their birth or death dates.
In addition, there had been a longtime political conflict between Bani Hashim and Caliphs which is manifested in Lady Fatima's will to Imam Ali (as) insisting that those who had displeased her (the first two caliphs) should not attend her funeral. Therefore, her funeral was held at night with the presence of only a few people.