The way I read it now is that there is a literal 144000, but that they are literally 12000 from each of the 12 tribes of Israel, just as the Bible actually states rather than being symbolic, a fulfillment of Gods promise to Abraham, this is then followed in verse 9 by the "Great Crowd" which I do not see as a different group, but is exactly the same as the 144000 but are the un-numbered group comprising the greater number of Gentiles who accepted Jesus. It states they have white robes and serve God day and night in his temple. Doesnt say these are the only Earth bound survivors of Armageddon.
Whilst man may no longer know the geneolgy of the descendants of the lost tribes, I am sure God knows.
This would help explain why there are far more than 144000 anointed, in fact I think all Christians in the last days who resist worshipping the Beast when it comes will be anointed.
I also think there will be ones who come out of the Great Tribulation who did not wash their robes in the Blood of the Lamb, these will provide the Nations that Jesus will Shepard with a rod of iron and who comprise the Nations that attack the Holy city at the end of the thousand years rather than Witnesses and resurrected who have gone bad and failed the "second test".
On top of which the resurrection doesn't happen at the beginning of the Thousand years so Dubs can train them whilst Sisters knit them clothing, according to the Bible, the general Resurrection happens after the thousand years:- And they lived and reigned with Christ for a[a] thousand years. 5 But the rest of the dead did not live again until the thousand years were finished