Again, your question is extremely confused and is mixing like three different phenomenon, but let me try breaking it down some.
The first thing you must understand is that for some speakers, they simply never will accent a devoiced mora, and the accent will always shift one mora to the right. This is not common among younger speakers but is fairly common among older people (40+?).
Young people are able to put an accent on devoiced mora, and usually do. But note that in these cases, it may still sound like they are putting an accent on the mora after it, esp if your ear isn't trained to hear this properly (and, in fact, the reason it sounds delayed is probably why older generations stopped differentiating them -- who knows, it could swing back to that at some point). In some specific cases, it is really hard to differentiate placing the accent, for example if you say ふ＼きん vs ふき＼ん with no surrounding context, they can just sound exactly the same despite your intention otherwise.
So basically, for example with 記者 (き＼しゃ）, there are three options:
- Intended to be pronounced [1], and realized as [1]
- Intended to be pronounced [1], but realized like [2] due to lack of sufficient auditory bandwidth/context to be able to realize the accent on the devoiced mora
- Intended to be pronounced [2], and realized as [2] (usually only the case for older speakers)
Now given the above, let me go through your questions.
クラス seems to have the initial mora devoiced quite often leading to クラス [2]
While it's possible that this would happen, in my experience ク is not devoiced, and regardless it is always a clear [1].
できない seems to turn into できない [3] with the き devoiced relatively often
I think this is a problem with your hearing, as a true [3] would sound very different from a [2] here.
星星 the し devoicing causing [3]
Yes, I would say it can sometimes sound like [3] (either due to devoicing, or おそ下がり, or even intentionally be pronounced like that depending on the speaker).
追いつく the つ devoicing causing [2] or even kinda [1]??
I think this is just your mishearing.
私記 is sometimes [1] or [2]??
Yes, this can be said either way. It is fundamentally [1] but the forward shift can happen like what I said at the beginning of this answer. Note that this is different from 式 , which is originally [2] and therefore is always said [2], never [1].
どこかに来た it seems like the き is devoiced and the nucleus falls on the mora before it
I can understand why you might mishear it, but basically any native speaker would just hear the accent fall in the right place.
BTW, due to the prior accent on ど, the accent on き is terraced and very minimal anyways, so it's not a good phrase to try and use as a test case here.
失礼します as [3] instead of [2]
A true [3] sounds different here and is not really correct. I think you just have some problem with つ maybe.
私たち seems to pretty much always be [2]
Yeah honestly that's how I think of it in my head too.
side note: 俺達 and 君たち seems to both be pronounced...weird...
sometimes?? like as [1] or [3] when they should both be [2]
Never heard this, I think you are just mishearing.
あなたたち i think is sometimes [2]? is that allowed?
Not only is it allowed, that is the correct pronunciation.
extra lil' thing... I feel like ドラゴン [1] is sometimes [2] in fast speech??
I don't think there is anything special about this word. It could be おそ下がり which can occur on any word but that is distinct from an actual accent shift, and does not sound like an accent shift to natives.
