It is a little odd, but I have a theory that Iga was beginning to accept that Legends, CotM, CV64, and LoD could be incorporated into his timeline. He's never come right out and said it, but references to those games had been popping up near the end of his tenure. Also, it would explain why he changed Lisa's death date. Having her die a couple years before Legends allows Dracula enough time to declare a fuck-this-world-war on everyone out of anger and using the slightly powerful yet limited resources available to him at that time.
1426
-Ryudomiru is born.
1433
-Sonia Belmont is born.
14xx
-Lisa, Alucard's mother, is condemned to death as a witch. Alucard() may have witnessed her execution.
1448
–After Lisa’s death, Ryudomiru(22) pledges his allegiance to Alucard(51) because Lisa had healed his parents.
-Ryudomiru is mortally wounded and turned into a vampire by the incubus Magnus.
-Alucard defeats Magnus.
1450
-Castlevania Legends
-Sonia Belmont(17) defeats Dracula(388) with the help of his son Alucard.
-Alucard enters a state of hibernation to remove his cursed bloodline from the world.
1452
-Isaac LaForeze is born. He has the natural powers of a Demon Forgemaster.
1455
-Hector is born. He has the natural powers of a Demon Forgemaster.
1456
–Trevor C. Belmont is born.
1459
–Julia LaForeze, Isaac’s sister, is born.
1476
-Castlevania III: Dracula's Curse
Instead of actually dying by Sonia's hands, Dracula pulls the old appear-to-be-dead-but-actually-escape-as-mist-trick that he would later use again on Christopher Belmont. This allows Dracula 26 years to bide his time, become more powerful, grow a larger army of monsters, and even tutor a couple of young Devil Forgemasters as generals. Also, keep in mind that Dracula's war had started long before Trevor set off on his quest. So we're probably looking at less than 20 years.