I am so sorry that you are going through this. It makes me FURIOUS that you are having to go through this with doctors that don't get it. It brings back all of my issues with one clinic we used. I don't have articles that I can point you to, but will look (and Mark had a good list already), but I do have experience.

Yes, symptoms can present beyond the 72 hours. If one was to look at my daughter's SCAT2 forms we filled out at every appointment early on - her symptoms were significantly worse 2-3 weeks into her concussion than the day after. New symptoms also cropped up during this time. Light/Sound/balance issues were present initially - but developed. Memory issues didn't present until 4-5 weeks into the process. (Perhaps they were there, but we didn't see them because of other issues.) My daughter also developed a tremor and stutter at about 5 week.

My daughter could pass all the memory tests of the SCAT2 two (numbers, word, etc) - but then couldn't retain new things from day to day. She was not able to learn new information and couldn't remember what she did day to day. On detailed testing, issues where show. She could also pass the balance tests - but at times couldn't walk down the hall without crashing into the walls.