Multiple streams same size

I been searching for the answer, but I can’t seem to find it.
In alot of movies I notice that there is 2 copys of the same thing. How do they differ? do I need them both? Is this common?
I could do trial and error, but would apprieciate any feedback.
I scanned thru them and they look the same, but I wouldn’t put it past david lynch to make them different.


I have included a pic
notice titles 3 & 4 are the same size as are 1 & 2.

I haved the same problem in “Kill Bill” Region3 Disc1,i backup two times… :sad:
My first backup used first main stream on this DVD movie and after finished burning,i test this backup on my dvd player,it show the wrong chapter

So i backup again and use second stream ,this time everything works fine… :o