Steve Burnside is alive.Let's look at the facts. Steve was infected with the t-Veronica virus. Viruses cannot live and reproduce in dead tissue. The t-Veronica can also only be spread by direct injection. Yet Manuela and some of the other experiments four years later are infected with it. It wasn't Wesker or his men just taking a tissue sample or some blood and leaving his body. They took his body. (After all, the whole place is gonna blow and nobody would want to be there when it does.) They would have a several hour long trip (at least) from Antarctica to wherever their lab is. In that time, the virus would die. This troper's working theory is that Steve was just unconscious, because he's the only Tyrant ever in this series to turn back into his human form upon severe injury. Every other one dies in that form or mutates.
The t-Veronica virus can make you really nearsighted.Steve apparently can't recognize Claire from ten feet away after he mutates, but he can recognize her from three feet away, even when he's going on a rampage. Or, you know, maybe he needed glasses or something before and the virus just aggrivated it.
Claire omitted a bit when she told Leon what happened during the events of Code: Veronica.That explains why Alexia kills Alfred. Alexia's high pitched voice is like nails on a chalkboard. The meeting at the end of Code Veronica X is cut to just them going back to grab Steve's body, only there's a message from Wesker, rather than the cutscene where he taunts them. That explains why the Twincest is lessened. That explains why Steve's not Canadian or annoying anymore. That explains why Claire sounds like she thinks Wesker's going to keep his word, while never actually saying it and Leon stating what Canon says right afterward.