It’s totally possible. I have the longest tenure at my current office, I trained my current team lead, but seniority-wise I’m still at the bottom. They base seniority on how important they think your job is or how much authority you have, not years of service : /
My boss reprimanded one of his senior employees (long tenure, team lead, stellar performance, overtime every day) in front of me for not choosing a different time of year to take a day off. It was the employee’s wife’s birthday, so don’t know how he could choose a different time of year. This is how that boss treats employees on a good day; he’s usually much worse. So yes…I’m totally sure the letter is real.