Four noble truths, any single being of mankind can invent, find the new truth other than that? Gautama Buddha found the traditional path of previous Buddhas and spoke about "The four noble truths". Nowadays, people cannot talk about/discuss the truth or falsehood of idea/notion/philosophical/religious entity. Did the current generation lose the ability to judge/determine/conclude the truth or falsehood of idea/notion/philosophical/religious entity? Or do we universally accept the idea that not a single living being be able to find/invent/prove that the new truth about the entities? Do we really have to remove the words truth and false from our dictionaries since we are not allowed to use in anywhere else?
If you will study in-depth, the Four Truths are a complete system in themselves.

Asking if there is a 5th truth to be invented is like saying if there is an additional step to the scientific method... i.e. such a person does not understand the scientific method in the first place.