A picture of the data plate would be very useful with AAM water heaters. Without that, though, I have several guesses, and 1993 is not one of them.
First, in some years, the first digit, a letter, is the month, so A would be January.
However, in other years, they used the first digit, still a letter, to designate the manufacturing plant.
Second, if the first letter is the month, then the following two digits, “20” is the year. Since we’re not to 2020 yet, I have to presume that the first digit, that A, is the place of manufacture. If I presume that, then the following two digits designate the week of manufacture, the 20th week, or sometime in May. If that’s the case, then the next two digits are the year. Sadly, that brings us back to 2020.
The last possibility with AAM water heaters is that the A is the month and the first 2 is the year, so either 2012, 2002, 1992, 1982, 1972. Pick one. When you have to pick one, the model number is useful to have, as well as the construction date of the house. If it “looks” vintage, vintage meaning that the house was built in 1993, then A2 probably means January 1992.