Both are arguably correct. There are plenty of dialects of English where the 'h' isn't pronounced, and even in dialects where it is pronounced (Irish English, for instance), 'an' is still used with 'historic(al)' and 'horrific', unless you're pronouncing the 'a' as stressed.
My dialect agrees with yours on this, with a phonetically unique form of 'an' which only appears before atonic /h/. Before a vowel, the /n/ is prefixed, the form before weak h has no nasalized vowel, normal for the article, and is pronounced [ɐn] as a single unit without the usual open [ɐ].
Untrue for my variety of English, which requires 'an' before 'h' unless it has primary stress, but retains the /h/ if it has secondary stress. We say the /n/ and the /h/ both in 'an historical.' Normative use tends to favor 'a' but 'an' is also correct. On the indefinite article, to avoid affectation, folks should spell as they speak.
As a native English speaker well-grounded in grammar, "an historic year" is absolutely correct, although "a historic year" is probably more common now. But back when I was in school several decades ago, the use of "an" was taught and preferred. It certainly should be accepted as correct!