that vertex above the cutout on a straight line could be avoided by using two quads at the front
(like this, also please round the decimals a bit...)
4 16 14.64 0 0 11.7329 0 -4.3501 11.7329 4 -4.3501 12.3182 4 -3.4794
4 16 14.64 8 0 14.64 0 0 12.3182 4 -3.4794 12.3182 8 -3.4794

Yes, I forgot to round

11.732902 0 -4.350097 still some left

This one is unified with the main part and will remain

but now the left mirrored subpart has slight mismatches...
when expanding the side 1-12cylo, the center is at 8.284 0 8.284, so what about
1 16 -20 0 20 28.284 0 28.284 0 4 0 -28.284 0 28.284 48\1-48cylo.dat (with invisible chrd)
and then patch it to the gap segment? then there are no mismatches at the subpart border...
(would some rect2p along the inside help? with a rect at the cutout? should be doable with slightly slanted rects)

Is this what you had in mind?

Maybe these should be edges?
2 24 13.03 8 4.95 13.03 4 4.95
2 24 11.12 8 2 11.12 4 2

hold: needs complementary condlines at the outside (at the ends of the outer cylos to the one not-prim segment with the step)
not hold: -does the inside 1-8cylo from the stud cutout also need one? (but that one is inside)
-still round the outside to 4-5 decimals
-maybe use rect prims for the inside (maybe even slanted ones)
1 16 11.72 6 -3.06 -.6 0 0 0 0 2 .42 1 0 rect.dat
1 16 11.12 6 -.32 0 1 0 0 0 2 2.32 0 0 rect2p.dat
1 16 12.075 6 3.475 .955 1 0 0 0 2 1.475 0 0 rect2p.dat
1 16 13.6363 6 5.3537 .6063 0 0 0 0 2 .4037 -1 0 rect2p.dat
1 16 16 6 13 0 1 0 0 0 2 3 0 0 rect2p.dat
-should this get cut out along the outside?
4 16 8.284 4 -8.284 -16 4 16 14.2426 4 5.7574 11.12 4 -2.64
inside would be then this:
4 16 8.284 4 -8.284 -16 4 16 11.12 4 2 11.12 4 -2.64
4 16 13.03 4 4.95 16 4 16 16 4 10 14.2426 4 5.7574
4 16 11.12 4 2 -16 4 16 16 4 16 13.03 4 4.95

Thanks for the review!
Switched conds to edges and added missing conds.
Applied rounding then unificator.
However I don't like using slanted rects so I keep it with quads.

that condline is definitely wrong: (control point on the inside)
5 24 14.64 0 0 14.64 8 0 12.32 8 -3.48 13.83 9.05 4.14
why is this a condline? should be flat (maybe intersect the cutout again)
5 24 14.64 0 0 12.32 4 -3.48 12.32 8 -3.48 11.73182 0 -4.349696

when I open that part in LDPE it seems ok but in the preview here the complementary condline from the 1-48 to the step is missing...
and that edgeline should be vertical (small differences in decimals)
2 24 12.32 8 -3.48 12.319 4 -3.479

I guess I should add extra conds for the 1-48cylo

if you remove (move to main) the stuff going to the inner corner you could reuse this for parts which use the same outer corners
18980.dat https://library.ldraw.org/parts/1322
30357.dat https://library.ldraw.org/parts/4349 (could need a rework anyways)

Yes I thought about having another subfile with common parts that could be reused for other parts you mention but indeed this is another project.

no need for another stacked subfile here, it should be easy to modify this into the common subfile (mostly by moving one bottom quad into the main file)