Yes, forlom, Shawn is 100% on the mark. As you may not be aware, the chips in the English carts and Japanese carts are EXACTLY the same. It's the BIOS in the actual Neo Geo system that determines whether or not certain things are seen or not seen. A prime example is the first Samurai Shodown. There is no way to get blood with the cart in a US system, but plug the SAME cart in a Japanese system (or a mod'ed system that has multiple profiles) and you get the bloody original version with which you are familiar from the arcade.
Also, the BIOS determines which title screen you get as well. Using the Samurai series again, in the English BIOS setting, the Samurai series is known as "Samurai Shodown 1,2, 3, etc." With a Japanese BIOS, you will see the Japanese title screen that will say, in Japanese characters, "Samurai Spirits," "Shin Samurai Spirits," etc.
I hope my answer is clear. If not, feel free to respond and ask for clarification.
And BTW, Metal Slug 3 is a GREAT way to start your Neo stash. It is a GREAT, GREAT game and much fun. Oh, and, to my recollection, the "Zombie Blood Hurl" from stage 2 is intact even with the English BIOS running.