NHK日本語発音アクセント辞典 lists 3月 as さんがつ{HLLL}, but it doesn't sound like a downstep on the first mora, but a bit like さんがつ{HHLL} to me. Are they both viable?
Is the 平板型 version also possible? Are these examples of さんがつ{LHHH} or am I mishearing it? 1, 2, 3
I don't know what 4, 5, 6, 7 are. I feel uncertain about putting them in either camp.
And the date that follows doesn't change the pitch pattern, does it? What about 3月号? さんがつごう{LHHHHH}?
At least phonologically, all your samples except #1 and #4 sound さんがつ{HLLL} according to my ear. However, a phenomenon called 遅下がり "delayed drop" is recognized in the Standard Japanese phonetics, that in some situations, the pitch drop point or the pitch peak falls on the next mora where the accent kernel is supposed to exist. Unfortunately, this is a relatively new topic that has not much research covered yet. Neither is known whether it signals an ongoing shift on the accent model of Japanese or not.
Recent papers:
Either way, it is known that 頭高型 words, like this case, are more likely to exhibit 遅下がり, probably because the Standard Japanese does not have a さんがつ{HHLL} type word to distinguish. If you put accent on the second mora, it only becomes さんがつ{LHLL} (while I don't think we have a word where ん carries accent).
By the way, #1 sounds as if the accent is neutralized on this word for some reason (trying to handle intonation?). #4 I certainly hear さんがつに{LHHHL} which is nonstandard in Tokyo accent, or perhaps affected by the speaker's dialect.
PS I forgot to mention that 三月号 becomes さんがつごう{LHHHLL} and the pattern applies to every 〜月号.
