There is a poem in witness. The poem says:

為證 uses wéi, "as proof."

The Tang king of the great realm, his grace and virtue vast, in the Way surpassing Yao and Shun, and all his people thriving.

堯舜, Yáo and Shùn, are the legendary sage-emperors of high antiquity and the fixed standard against which every later ruler was measured — so "surpassing Yao and Shun" is the highest compliment the vocabulary allows, and correspondingly cheap.

Four hundred death-row prisoners all left the gaol; three thousand grieving women were let go from the palace.

怨女, "resentful women," is the established term for palace women kept from marriage — the resentment being understood as the natural consequence of the arrangement. The couplet puts the amnesty and the release into verse, four hundred against three thousand.

Officials throughout the realm proclaimed his long life; the ministers in court hailed the 'prime dragon.'

上壽 is to raise a toast for long life. 元龍, "prime dragon," is a flourish for the sovereign; 朝中 is cháo zhōng, at court.

One thought of a good heart, and Heaven surely blesses; the shade of his fortune shall pass down through seventeen reigns.

天應佑 is "Heaven will surely protect"; 應 is yīng. 福蔭, fú yìn, is the shade cast by good fortune, in which one's descendants get to stand — the Chinese idea that merit shelters a family the way a tree shelters ground; 蔭 is yìn. 十七宗, seventeen reigns, is the couplet's promise of dynastic endurance, and it is Cuī Jué's parting bargain restated as poetry.