Acts tells us that Matthias was numbered with the eleven apostles. Twelve is the number that is associated with Gods government in scripture and here we have an interesting parallel between the 12 apostles and the 12 tribes of Israel.
The list of tribes in Revelation 7 adds the tribes of Joseph and Levi and leaves out the tribes Ephraim and Dan. Is it possible that both Matthias and Paul were apostles? Two of them would be left out in Revelation 14:21.
I just never quite understood why Paul was called apostle and the scripture seems to say something different. I sure get a lot of different answers. You ask another question, what happened to those 2 tribes...
Its been quite a while since I read Revelations but will have to reread it again...along with that part of the OT that list the tribes. You add something that I had not thought of IE: number of tribes listed in the beginning and end of the books. :O)
There is zero evidence in the scriptures that Mathias ever functioned as an apostle. There is also no authorization contained anywhere in the scriptures for men to select apostles.
YHWH has always selected his own, without help from corruptible men.