Hi Kashmir,
I am a big fan of yours. Though my views are very radical(In that I don't think Congressmen need to be involved in USCIS work(e.g for delays and handling personal cases, not for making laws) (This situation is pathetic

), I am an extremely law abiding citizen(I always fill in the customer-complaints feedback forms

) . I plan to start my full-time involvement in this community with you from next year(This year I have too many things on my hand, sorry).
Now coming to the point,
I will search for something for that LC statement. It is true that this is tricky.
But it can still be proven that LC has immigration intent.
Can anyone give me a single valid reason otherwise.
LC application is not a H1b application(I am thinking out loud, you know already!).
H1b does not have an immigration intent, LC really starts the process. Why would someone go through the process?, It is definitely not to get their Education and Experience evaluated, it is more than that.
I agree with everyone who says that the Labor PD has to be considered as the date of intent. Otherwise I-485 only gives an intent to become a GC holder, and nothing else, though it is a means to become a US citizen.
If you see in one way LC is giving as much an intent as a I-485 to be a Permanent Resident. Intent to become a citizen is a totally different story.
There are people whose LC is denied and later approved through a different employer. I wish they could be helped, but I don't think they can be.
BUT
Suggested dates for start of the 5yr count, for citizenship application eligibility can be:
1. Application of valid Labor approval FOR original LC holders(EB2, EB3 etc).
2. Application of I-140(approved later) FOR substitute labor applicants and EB1s
3. Application of I-140(approved later) FOR L1 and other visa holders who do not need LC.
Instead of suggesting, I should be drafting(like you), but I have my shortcomings. I have put forth the points which might help. I might be wrong, If I am, I am willing to hear that from others.