Serious question: Why A2 is not 2A?

All androids I see they've their numbers first then the model type they're, so why A2 is the exception? (⁠;⁠;⁠;⁠・⁠_⁠・⁠)(⁠•⁠ ⁠▽⁠ ⁠•⁠;⁠)ヘ⁠(⁠。⁠□⁠°⁠)⁠ヘ

All androids I see they've their numbers first then the model type they're, so why A2 is the exception? (⁠;⁠;⁠;⁠・⁠_⁠・⁠)(⁠•⁠ ⁠▽⁠ ⁠•⁠;⁠)ヘ⁠(⁠。⁠□⁠°⁠)⁠ヘ