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
Unfortunately not all local listings are inputed into trulia unless a specific company and/or agent decides to do so. Some of it is through IDX (information data exchange) however this system isn't perfect. Also, if an address is not disclosed, the marker for that property will show up in the middle of the zip code it is located in.
Hope this helps. To find out more information on the homes you have driven by please visit the website below. Just do a local search (of all homes listed) and hopefully you will find the answer you are looking for (price, beds, baths, etc.).