In Surah Rum, why did the verse say that the Byzantines will overcome in three to nine years, according to the Saheeh International translation, instead of giving the exact number of years since Allah SWT has the knowledge of the unseen?

Qur'anic VerseSurat al-RumDivine KnowledgeIlm al-Ghayb
In Surah Rum, why did the verse say that the Byzantines will overcome in three to nine years, according to the Saheeh International translation, instead of giving the exact number of years since Allah SWT has the knowledge of the unseen?
Sayyed Mohammad Al-Musawi, Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to... Answer updated 3 years ago

Quran has informed about the future in a miraculous way after the defeat of the Romans. Usually the defeated nations can not stand up strongly in short period to defeat those who defeated them. Allah said in Sura Rum: And after being defeated they (Romans) will defeat (their opponents) within few years Bidh'i بضع سنين which is between three to nine or ten years. The exact number of years was not mentioned because the victory of the Romans on their enemies took few years through many battles and was not in just one year. 
'The battles took few years till the Rum defeated their enemies. Quran said: في بضع سنين Within or during few years, which is exactly what happened.

Wassalam.