Regarding your last bit about student years not counting towards C permit for spouses of Swiss citizens, you are misunderstanding that. This refers to attaining C permit "under art. 42 al. 3", which is a preferential treatment giving right to C permit after 5 years of marriage and living together (as opposed to the normal 10, and as opposed to other circumstances where a C permit may be granted , but not by right), where previous stays before the marriage don't count towards those 5 years. The spouse of a Swiss citizen can still get a C permit under the normal general conditions if they fulfill the conditions earlier than under this preferential treatment. For example, if someone has lived here 8 years including study years and could get C in 2 years, marrying a Swiss person and getting family reunification doesn't reset the clock. They can still get the C permit after a regular stay of 10 years under the normal conditions, they just can't get it under the preferential treatment. That is clear in the jurisprudence (ATC 122 || 145).
Regarding your first point, well, no, I'm sorry, it very obviously refers to the stay. That's what the sentence says. Any Italian or French speaker reading the version in those languages (the English version has no force of law, the national language versions do) would understand it that way, because it's the only way it works grammatically as a sentence.
Art 34, al. 5
"Completion" is also only in the English translation which again has no force of law. In all national languages it's only "once they are ended". Nowhere in the law or directives does it say anything about graduation with regards to this. It simply doesn't. You seem to be conflating the counting of student years towards C with the relaxed conditions to access the workplace after graduation. Those are completely different things, although of course ultimately connected.
I know there is no explicit option mentioned to jump from L to C, that's why I repeatedly said I know there's a good chance I don't get it now. There is however this ambiguous addition in the directives
Directives 3.5.2.1
That does sound like you can jump from L to C if the L is considered long-term. Which you've pointed out yourself in your first comment. But of course the fact that it's family reunification complicates things and makes it maybe likely I don't get the C permit. Again, and I don't know how many times I have to repeat it, I know this! That isn't the question I'm asking!!
We are in any case getting at least a B permit at our next renewal (that's what the cantonal rules are, explicitly. With a permanent, indefinite contract you get L for 24 months, then B. That's both written in the policy and has been said to us by everyone we talked to at both the Commune and migration office). So maybe they make me go through hoops and give me a B only so that I can then immediately reapply for C, I don't know.
Maybe I should just not bother applying for the C permit, and apply the day I get my B (which should be around the later of the three dates I previously mentioned).