There are two things worth noting:
1. The original value for org-log-into-drawer is nil.
2. There seems to be no value that would enable movement of old records
into drawers.
So assuming somebody just discovers this variable(like me), decides that
drawers is what he wants, now he has to move all those old entries
manually. That's not too much work, but we already have a better
behavior example in org-clock-into-drawer.
It's still a rather minor issue, by all means...
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Best Regards,
Nikolay Kudryavtsev