Was "The Book" filmed earlier than season 5?

Yes, according to notes on wiki (part of the episode guide for this series), The Book was a fourth season episode that was held over and not aired until the fifth season. 'Black Widow' was also made during the previous season and delayed for broadcast.

So yes, we have already had episodes that reference Marsha's porsche which she bought in this one (like the episode where Heather is blamed for scratching it).

Fox, the owner of the series and the studio responsible for selling it into syndication, should have put 'The Book' into the correct order and aired it with the other season 4 episodes so the continuity is as it should be. 'Black Widow' seems to work as part of the season 5 offerings. But 'The Book' is glaringly out of place.