Campaign Progress Lost?

so Today in the middle of my legendary run I noticed that I lost the first to levels of my campaign progress. but I had all of my other legendary levels.

I am desperately trying to get the legendary ending but I know you have to beat the entire campaign on legendary. That would be a true pain for me to go back and repeat the first 5 levels to unlock the ending.

But I truly need to know can I unlock it if I just keep on playing through or do I have to go back and repeat the first % I have completed