Confusion regarding "〜てからでないと・・・"


recently I purchased a grammar book to help me prepare for the JLPT N3. One of
the constructions I have come across is "〜てからでないと・・・." And I understand it's
basic function (I think...). From what I understand it means something like
"Unless A occurs B will/can not occur." I have come up with a few example
sentences I'll place below. Please feel free to tell me if I have made any
mistakes in my usage.

私は日本語がペラペラになってからでないと、日本の大学院に行けません。

毎日勉強してからでなければ、しけんにごうかくができません。

アメリカの人口がデモクラットのだいとうりょうをえらんでからでないと、しゃかいせいぎはしんぽしません。

However, after a few days of letting this grammar pattern mull around in my
head I started to wonder if there are any inherent difference between the
above grammar pattern and using a negative conditional followed by a negative
main clause. For example is there a (big) difference between my first example
sentence above and the following sentence:

私は日本語がペラペラにならないと、日本の大学院に行けません。

I've tried doing some preliminary research on this grammar point but have not
been able to find much online in the way of explaining its nuances. If you
know of any resources that got into this further I would greatly appreciate
them.

One thing I was also wondering is if this grammar would be something used in
spoken language or is it more for written language? Also, if anyone knows a
site the clearly identifies which grammar points are mainly used in written
and spoken language that would be awesome.

And finally if anyone could help me understand the construction of this
grammar point that would be wonderful. From a literal perspective it seems
like it means something like "(〜てから) after doing some verb (でないと) if it is
not" or rearranged "if it is not after doing some verb." Like I think I can
see where the are going with this but it is just not coming to me that
intuitively.

Again, any help you can provide is completely welcome and appreciated. :-)




I believe that the ～てからでないと pattern has more chronological order implied. The
basic meanings are similar.

一生懸命勉強してからでなければ、試験に合格できない。  
一生懸命勉強しなければ、試験に合格できない。

Both have the same basic meaning of "If you don't study you won't pass". But
the first one has a nuance of "taking the test once you have studied".

Similar idea to 勉強してから、試験を受けないと合格できない vs 勉強しないと、合格できない。

