I'm wondering if I should mention this when I undergo my review, omit this detail, or mention it vaguely? (Side note: I have a copy of the offer letter).
Sure, but be prepared to actually take the offer if your company rejects it. However, since you already rejected it, it sounds like you have no fall back option. My advice is to seek employment where you get paid the amount you want then say goodbye to your current company but allow them to match the offer before you go. It's far better to have an option than it is to simply ask and hope because from my experience, you will not get a significant pay raise.
As an aside, you should be getting 2-3% raises each year. If you're not getting that, I would ask for that, as well as any previous year they missed.
As a final point, if you are currently a level X person, ask your boss how you can get to X+1 level and you are interested in working towards that and whatever pay raises that may encompass it. I think that approach is benefitting to you and your company and you get to work towards a goal.