These are very common "mistakes" to the point that descendants choose one over the other and they all think they own the "correct" spelling. The "Gil de Taboadas" almost disappeared and are now simply "Gil" or "Taboada". You wouldn't believe the different ways I've seen my last name written (chuckle). The "y" between the paternal and maternal last names is merely a convention and there's nothing right or wrong about it. Toh-may-toh, toh-mah-toh, poh-tay-toh, po-tah-to, not a gator, just a gato... ha ha But keep documenting it because it may explain a lot of things later!