Use of 不 for negation in the 不曾...過 pattern

Question

In Emil Wakin Chau's song 朋友 péngyou, there is a line:

朋友不曾孤單過。
péngyou bùcéng gūdān guò.

I think the meaning is something like "friends haven't (ever) been/felt lonely".

I find this use of 不 bù alongside 過/过 guò odd, as it goes against the well-known rule that guò sentences are negated with 沒 méi. But I assume the song lyrics are correct and, in fact, I've found that 不曾 bùcéng appears in some dictionaries, and the Chinese Grammar wiki site[1] says that both 不曾 and 未曾 can be used to negate a past experience with guò. I was wondering if this use of bù with céng, or with the disyllabic version 曾經 céngjīng, is as common or acceptable as using méi(yǒu) or the formal 未 wèi. Consider the following alternatives:

朋友沒(有)孤單過。(1)
朋友沒(有)曾孤單過。(2)
朋友沒(有)曾經孤單過。(3)
朋友未孤單過。(4)
朋友未曾孤單過。(5)
朋友未曾經孤單過。(6)
朋友不曾孤單過。(7)
朋友不曾經孤單過。(8)

My three questions:

1. Are all these versions acceptable?
2. Is the meaning the same in all the valid cases?
3. Are there any other cases of 過 guò sentences being negated with 不 bù and not using 曾 céng?

[1]: https://resources.allsetlearning.com/chinese/grammar/Expressing_%22once%22_with_%22cengjing%22 no

Answer 1

(1)朋友沒有孤單過。- Friend(s) has/have not left alone before(過).

X (2)朋友沒有曾孤單過。(Note, "朋友沒曾孤單過。" could be acceptable to others.

X (3)朋友沒有曾經孤單過。

(4)朋友未孤單過。- Friend(s) has/have not left alone before(過).

(5)朋友未曾孤單過。- Friend(s) has/have not ever(曾) left alone before(過).

X (6)朋友未曾經孤單過。

(7)朋友不曾孤單過。- Friend(s) has/have never(不曾) left alone before(過).

X (8)朋友不曾經孤單過。

Summary of the valid negation patterns: "沒(有) 去 過", "未(曾) 去 過", "不曾去過". Note the latter two negate the phase "曾經去過" ("不曾經去過" is grammatically incorrect.)

Answer 2

从未孤单过

未曾孤单过

从未曾孤单过

从未曾经孤单过

没有孤单过

从没有孤单过

没孤单过

从没孤单过

曾经孤单过

All the above are possible.

Answer 3

Well, first of all, logically, they are equally the same. Only, they provide different emphases.

朋友沒(有)孤單過。(1) 朋友沒(有)曾孤單過。(2) 朋友沒(有)曾經孤單過。(3) 朋友未孤單過。(4) 朋友未曾孤單過。(5) 朋友不曾孤單過。(7)

Only these two are not "grammatically" correct:

朋友未曾經孤單過。(6) 朋友不曾經孤單過。(8)

未曾 = 不曾 is kind of idiomatic expressions in written Chinese, but not 不曾經, which is kind of awkward expression, at least in mandarin.

This remind me one thing though: Once, I've met a Belgian young man who spoke Chinese fluently, and he said he has only been in China for a year, and study Chinese for about 2 years if I remember correctly. I was quite surprised on his talent on language and how efficiently he learned Chinese, and he told me that oral Chinese is actually very easy to learn since the gramma is very simple and there's almost no rules at all, only words and context matters.

This conversion put me into thought, and I'm kind of agree.