[Physicist]

You're missing the point. The measurement of the speed of light at SN1987a is independent of how long ago it occurred. It only depends upon how far away it is. (Even YECs admit that distant galaxies are far away.) However long ago it occurred, the speed of light hasn't changed since then.

[bryan1276]

The speed of light decays. It may not be a measurable decay in 14 years of time, which is what it sounds like your talking about. Since you can't measure any decay in 14 years then it doesn't decay.