Hi, It’s the husband of Tuppence here.
Let me put this in very simple terms for all to understand. Over a period of 300 years or more, the speed of light has dropped by more than 1500 km/s. If you wish to attribute this to changes in the measurement of the second, this is equivalent to saying that the length of the year (365.25 days) has changed by 1.82 days over this period. This is nowhere near what has actually occurred. As pointed out by physicists, the changes in the speed of light are far greater than any adjustments made to other physical quantities such as the second. Therefore the decline in the speed of light cannot be accounted for by these adjustments.
I trust this clarifies the situation.
The Husband of Tuppence.