I've only really worked with the 70MPW plan but I assume the others follow a similar structure. The way I look at the 18-week 2Q plan is that it's made up of a repeated 3-week block that changes a bit over the course of the program. When I shorten the plan I usually cut out one or more of these blocks, or I just look at the overall distribution of workout types and design my own 12 - 15 week progression that follows a similar structure (maybe just for part of it).
The basic 3-week block has 6 quality workouts in (M, T, T, I, E, T) order. Typically these workouts each have the same structure. For example, the T workouts are:
1: long warm up -> T intervals with 5:1 rest -> short cool down
2: short warm up -> T interval(s) (with 5:1 rest) -> long block of E -> T interval -> short cool down
3: long warm up -> T intervals with 5:1 rest -> short cool down
Weeks 1-3 and 4-6 follow that structure exactly.
Weeks 7-9 and 10-12 are similar except that at the end of week 9 Daniels starts replacing some T work with M work (sometimes listed as optional) and incorporating a couple workouts with both M and T pace segments where he previously had pure M or T workouts.
Weeks 13-15 get back to the original structure except that he replaces the last T workout with a second I workout
Weeks 16-18 I view as a taper block. It has the original structure except the I workout is replaced with a low volume M + T workout.
So to me the plan is basically just repeating this 3 week cycle, trading some T work for M work and/or incorporating mixed T+M workouts later in the plan, hitting the last v02max workout 3-4 weeks before the race (including an extra in place of T work), and tapering down workload as he suggests over the last ~4 weeks. Also, it looks and feels to me like the hardest work is done about 7-5 weeks out from the race, so I try to maintain that as well, although I've also had success reducing that block of work a bit and hitting a peak (hardest) workout 4 weeks out from the race.