Incerdibly frustrating I know.
Shelley touched on the IDX a bit and that is pretty much the reason for the lack of information on some homes. Yes, sometimes Trulia has not picked up the info yet but actually a Brokerage decides upfront if the information of their listings will be shared through the IDX. If the Brokerage opts out of the IDX then the MLS will not allow websites such as Trulia to use all of the information from a listing.
Good luck with your search