Efficient way to concatenate strings to find specific split up values
If all the words are going to be English words, you can run all the words through a dictionary. If you find any non-dictionary words at the start or end of the sections and you are unable to find the "key", you can just combine those words until the key is found.

Alternatively, you can trivially just combine the the words (once) at the start/end of sections until the word is found. I don't believe this will to too inefficient computationally since the described sections are quite large.