So going through the manual,
-the original type of pistons in w115 240d would look like :
https://www.peachparts.com/shopforum/attachments/diesel-discussion/94422d1312305275-616-rebuild-options-img_0507.jpg
They are used with flat tip prechambers, the one that you showed in your photo.
Later MB introduce the star-shaped combustion chamber pistons with two different type of recesses - flat and rounded(for the so called "uprated engines" in the manual) :
Flat tip PC's are OK with :
-pistons with round shaped comb.chamber (as originally)
-and star shaped Cchambers having the
flat recess (type C)
..........
Round tip PC are to be used with star shaped chamber with rounded recess (type D) .
They should not be used with star shaped , flat recess chambers (Type C)
...or with the round combustion chamber cavities (like the older type om615/616). These are only in om615/616 context !
However, the way I read the manual ,the flat recessed star chambers (Type C) are applicable only to om615's pistons .
So your PC's seem to be unsuitable for the NE pistons that came with the block (because they probably have the rounded recess-and that is IF the star-shaped flat recess of type C ever existed in 616-617 pistons ).
I tried to look closely at the your photos,also checked some other,like this genlteman here:
https://www.flickr.com/photos/govert1970/albums/72157625987974204/
Note that he upgraded to the round tip prechambers. The new pistons look to have a rounded "star" recess(type D)...but light and photo angle play tricks...
Also , the NPR catalog lists only 1 type of om 616-617 pistons, page 202 :
https://www.npr-europe.com/wp-content/uploads/2024/08/P7-Katalog.pdf
They probably went with the most "popular" option, the "rounded" recess star (for later type, rounded tip PC's)...
Also, some pics from YT of a guy restoring a w115 om615 using "star"and flat recess pistons .
Note that he is keeping the original flat tip PC's .
Check first the type of recesses yours have...but judging by the manuf.catalog they're probably rounded.
A thread with part #'s :
http://www.peachparts.com/shopforum/mercedes-parts-reference-library/315201-om616-916-extreme-rebuild-parts-list.html
http://www.peachparts.com/shopforum/diesel-discussion/170391-different-type-prechambers.html
6160100152 - om616 prechamber , round tip, 616/01 marked .
Well...that's what I could gather . Hope that someone who's been through it would chime in.
Note the star shape in the Service manual and the currently offered pistons differ ...hm...