I'm thinking that Originally there was a comandment about a Father having sex with HIS daughter (try all you want 18:17 only relates to a Man having sex with a woman and her progeny). But the Bible by Committee werent comfortable with that since it would cause an conflict with the Grand story of S&G, and the escape of Lott.
Is this from the notes they kept of their meeting, or an assumption you're making about the decisions (based on an assumption you're making about the story, based on an assumption you're making about the motives of God)?
18:1 handles it just fine. 18:17 handles it just fine, as having sexual relations with a man's daughter would and could only be accomplished after having sexual relations with the daughter's mother - thus having sexual relations with a woman and her daughter. You know, the thing specifically spelled out as not to do, and includes step-children in the way it's worded (sorry, Woody Allen). Just because the specific words you want to see there aren't there doesn't mean the specific action is denied (it is!).
Here you have this detailed story about how God lays waste to 2 cities for not following his edicts and commands, and the One guy that gets saved (because he is a Pillar to look up to) is involved in the type of Hedonistic acts that caused S&G to be wiped out.
If your trying to get a theme out, wouldnt it be in your interest to minimize that your Hero is just as corrupt as the Sinful towns he was saved from? Easiest way to do that, remove any reference where the Hero broke Gods commandments.
Its obvious that something has been removed, or not told, since the ONE situation that is not included in your LEV 18:XX verses is a Father having sex with HIS daughter. ALL other situations are expressely called out EXCEPT for that one.
I think you're mixing a couple of things here. S&G is about God's wrath towards the incredibly and intentionally sinful (as opposed to the occaisional and repented sins we all have). Lot is about proving that, even in His wrath, He does not always take out everybody and wipe the slate clean (Noah also proves this). Lot with his daughters is about the origins/lineage of two nations of people, albeit with a sinful start. And, intention being a huge part of sin, Lot being drunked up by his daughters and presumably effectively raped makes him not responsible for his sinful action, but his daughters responsible.
You also need to remember that the Bible (according to most on here) was written for the people at the time (begs the question about where's today's version?) are you trying to claim that the verses EXPRESSLY state EVERY possible combination of family you can not have sex with, but on this ONE particular instance its inferred?
It's not inferred, it's specifically spelled out - not with a woman and her daughter (which, by physical limitations of reproduction, includes a man and his own daughter - so obvious it is not needed to be spelled out for a third time, after 18:1 and 18:17).