Backwards Tythe Process

[Wexflyer]

I was just looking at the tythe valuation records for the parish of Kilcomb, diocese of Ferns, after a gap of some years.
I was reminded that the process seems backward to me. Consider:
Commissioners certificate, giving amount of composition, December 1824.
Special Vestry to approve composition, January, 1825.
Survey and applotment of parish, May and December, 1826.

In other words, the actual applotment was completed 2 years after the value was set. Seems backwards. I would have though the value would be the product of the valuation, not the other way around!! ?