I believe it's certain that the text for the "bad" (gray sky, 15 days or longer) and "average" (blue sky, 8 to 15 days) endings was switched around. I know this because in the "bad" ending, amid a gray sky, we see Dracula's grave by itself, and in the "average" ending Simon is right there kneeling at it.
The text we see in the "average" ending should really have been in the "bad" one...
"Although the confrontation between Simon and Dracula has concluded, Simon couldn't survive his fatal wounds. Transylvania's only hope is a young man who will triumph over evil and rid the city of Dracula's deadly curse."
Whereas, what we see in the "bad" one should have been in the "average" one...
"The battle has consummated. Now peace and serenity have been restored to Transylvania and people are free of Dracula's curse forever. And you, Simon Belmont, will always be remembered for your bravery and courage."
What I would like to find out is what parts of the code in the ROM to change to make the text for the bad ending appear in the good one, and vice versa.