Death sentences in Florida and retroactivity of the U.S. Supreme Court precedents

In Marbury v Madison, a seminal 1803 case, the U.S. Supreme Court has held that an unconstitutional law is void.

"Void" means a nullity - like the law has never been made.

It means that, once a court of law pronounces any law unconstitutional, it is as if that law has never been passed, and has never been legal.

In January of 2016, the U.S. Supreme Court found the Florida death penalty law unconstitutional.

It should mean - under Marbury v Madison - that the Florida death penalty law is void and a nullity, as if it has been never enacted, and that all death sentences under that law are similarly void.

Yet, today the Florida Supreme Court reversed only those death penalty sentences that were made after 2002, or whose appeals were still pending in 2002 - indicating that the decision of the U.S. Supreme Court will not be made retroactive before that date for other death sentences.

Which raises an issue - did the Florida Supreme Court invent a new definition for "void"?

And, how many more people should be unlawfully executed, in addition to the one already unconstitutionally executed (Ronald Bert Smith Jr., in Alabama, even though his death sentence was imposed by a judge and not a jury, in contradiction with the January U.S. Supreme Court precedent), because their sentences were unconstitutionally made "too long" of a time ago?