Why did the floor drop so dramatically,. Was the old one layered?

In that case above I think I would have brought the jamb down, cutting the profile out of MDF or something. Looks like 1/2" would have slid right in. That's just my approach though. Your skills with a miter obviously out pace mine so I avoid miters if possible. In the immortal words of Clint, "A man has got to know his limitations."

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