If the garage was included in any prior sale there would be a contract reflecting that and a deed supporting the inclusion of the garage. Since it appears no deeds included the garage, it wasn’t included in any sale.
Title insurance would do you no good since the garage was not deeded to you. It removes it as being a title issue and leaves it at a contractual issue. So, does your contract include the garage? If not, I’m not seeing a great case for you. If it did, you still would have no right to claim title to the garage since the seller didn’t own it but you may have an action against the seller for claiming to sell you something that he didn’t own. All you would be entitled to based on that would be money. How much would be up to the courts to determine.
Contracts aren’t recorded in any state I’ve dealt with. I can’t say whether they are in your state but I wouldn’t expect them to be.
As to the deeds; so far it appears no deed showed a transfer of the garage to any buyer of your unit.
If the attorney believes you might somehow be entitled to be able to claim title to the garage, it would be quite a considerable amount of work to show through all sales that was the intent and it was some error that it was not included on the deeds. The cost to research and attempt to change all of that could be quite expensive.