The “immediately before beginning the reserve or flight duty period...” just means they can’t give you your rest period, then have you teach a 4 hour ground school class, then start an FDP out to table B limits. They’d have to include the ground school as part of your FDP.

The “10 hour rest period” is still not limited to only 10 hours. It goes back to the most recent duty you performed for the company, and the 8 hour sleep opportunity just has to be in there somewhere. Perhaps it would have been more clear if their sentence read, “The (at least) 10 hour rest period must provide the flight crew member...” but I’m sure they felt that would be redundant and a bit cumbersome.