What is the criterion for the argument of "Sharia is still ongoing," and why is this same argument not used to say that something is recommended in a matter where there is a command of obligation (in one hadith) and non-obligation (in another hadith)?

It is observed that Shar'i rulings may be legislated in stages, and what has been finally established is acted upon. Al-Zuhri said: "One should take the last and latest of the Prophet's actions (peace and blessings be upon him)." Nevertheless, texts should be reconciled whenever possible, as reconciliation takes precedence over preferring one over another, and implementing all texts is better than neglecting some. There is no real contradiction between Shar'i texts; if it appears so, it is a superficial contradiction, and effort must be exerted to remove this contradiction through reconciliation and harmonization. If reconciliation is not possible, the later of the two texts should be adopted; if the later text is unknown, then one should be preferred over the other based on the various grounds for preference.