How are they either observable or reproducible? Sure, when alive they can be interviewed, but how can their claims be verified? Anyone can make any claims they want, but without independent observation and testing, how are they to be verified? Until they're objectively verified, mere claims don't qualify as real evidence.
They are observable since they come in the form of a man.
They are reproducible since they come one after another...
I never said that their claims can be verified. It is up to each individual to determine if their claims are true.
As for independent observation of the Messengers of God only those who saw them when they were alive could observe them.
As for testing the Messengers, below explains the way we test them.
Bahá’u’lláh asked no one to accept His statements and His tokens blindly. On the contrary, He put in the very forefront of His teachings emphatic warnings against blind acceptance of authority, and urged all to open their eyes and ears, and use their own judgement, independently and fearlessly, in order to ascertain the truth. He enjoined the fullest investigation and never concealed Himself, offering, as the supreme proofs of His Prophethood, His words and works and their effects in transforming the lives and characters of men. The tests He proposed are the same as those laid down by His great predecessors. Moses said:—
When a prophet speaketh in the name of the Lord, if the thing follow not, nor come to pass, that is the thing which the Lord hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.—Deut. xviii, 22.
Christ put His test just as plainly, and appealed to it in proof of His own claim. He said:—
Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. … Wherefore by their fruits ye shall know them.—Matt. vii, 15–17, 20