I've never learned bopomofo in earnest, and for pinyin I just memorized everything that felt like an exception to me, even though it might have some internal lo

I've never learned bopomofo in earnest, and for pinyin I just memorized everything that felt like an exception to me, even though it might have some internal logic. For example, I guess that the "a" in "yan" is different from "lan" because "yan" is its own coda, whereas "lan" is "l" + "an"?