You should only have to put in one word in the file name for Spotlight to find the file. If you are searching using multiple words then too many or too few spaces between words in either the actual name or search argument can prevent the file from being found. (I'll give you three guesses how I know that and the first two don't count 🙄)
If one word doesn't find the file there is the possibility the Spotlight index has become corrupted and needs to be rebuilt. You will find instructions for rebuilding the Spotlight index in
this Apple Support Document.
