Its supposed to mean the same thing in the show I'm sure. Apocalypse has it so that Ashford created it to save his daughter. The Final Chapter shows that the T-virus existed earlier because of that thing with the school kid that led to Marcus' death. The novelization explains the discrepancy: Marcus discovered the Progenitor Cell which Ashford adapted into the T-virus but that's considered non-canon. Its probably a retcon, the origins of the T-virus.
The novelization is not part of the Anderson movie canon; nor are the others (DeCandido did whatever and used alternate character names, while Shirley made a universe for Retribution which contained the movie plot; and original story and elements from the DeCandido universe).
The most reasonable explanation for what happened, I think, is that Anderson changed his mind over the T-virus history, whether failing to secure the Charles Ashford actor or just wanting to reference Zero, which he wrote Apocalypse too late to do. You can always just fanwank that the two worked on it together and there was a difference of opinion as to who the creator was.
True but aside from adding the part at the beginning showing what happened at the White House (which makes a lot of sense) and showing Alice always thinking of Becky and her safety, really nothing's changed.
I just flipped through the ending and literally the final chapter of the novelization is from Becky's POV showing how she was put in a safe room by a "nice woman" who Alice had left her with (I'm guessing Jill or something similar) and there was quaking like an earthquake and the room collapsed but she was fine and couldn't find anyone else afterwards. At the end, Alice finds her with the help of the Red Queen and a satellite. I'll update any information from the others fates at the beginning of the novelization but that last bit made it sound like Wesker betrayed them almost as soon as they reached the White House and there might've been a nuclear strike since Alice warned Becky against drinking the water in Washington. She hesitated before saying it might not be fresh but that could've been because Becky wouldn't understand what really happened.
I know but there tend to be major differences there. I went through this one over a few hours time and there really isn't much difference. Its based on Paul S. Anderson's screenplay according to the front of the novel and this is a totally different author. The first chapters of the book which show the White House battle confirms the deaths of Leon, Ada and Jill by the way. Along with being a trap for the last remnants of humanity, it was actually a battle between Albert Wesker and Dania Cardoza, an Umbrella higher-up after his position. She was what he wanted to use Alice as a weapon against. After Alice killed Dania by telekinetically crashing her V-22, an antidote Wesker injected her with alongside her powers kicked in, stripping them again. Hence why she had no powers in The Final Chapter. The T-virus was still within her though but inert which is why the anti-virus had an effect on her. Part of Dania's plan had the Undead army (which was controlled by her through technology) merged into one massive creature that only lasts for 15 minutes. That's what destroyed the White House. Wesker left Alice to die by that thing after she took down Dania who later turned out to be a clone of the real one designed to lure Wesker into a false sense of security so the real one could kill him in the Hive. That failed by the way and he killed her. Besides the addition of the Dania storyline there were very few differences as far as I can tell. The only big one is that the anti-virus was instantly effective on all the Undead everywhere and did not require years to spread across the globe. It also explained the countdown which was when the Umbrella forces across the world were to simultaneously attack the three remaining human settlements in Paris (the Eiffel Tower I think), Kyoto and Raccoon City. The Isaacs clone simply jumped the gun because he was so eager to get Alice. The book also showed that Wesker retained his abilities (he chose not to take the antidote he gave Alice simply because he liked the power of them) though he constantly battled the T-virus for control. When he bled out, all of the T-virus in his blood left him with his blood which is how he was able to die.