I have split sets, however romcenter wants to add samples to the rom zips.
1944.zip is complete (15 files)(and works in MAME), however rom center wants to add dl-1425.bin ("available in another game") to the 1944.zip.
1944 is yellow and "Rom need fix".
This is the same for 3362 of my 36000 roms.
1944d.zip contains nffud.03 & phoenix.key and is green - no fix needed.
Settings -> Merge Mode:
Sample: Split (with sample folder set)
I am able to run a test version of Romcenter if this is a bug.