The issue here is that what "one" item number is isn't clearly defined while being arbitrarily ruled in this moment. SLPS 02000~3 as one item number is no different than the examples I've presented. Four of five are abbreviated, though the formatting means varies.
SLPS 02000~3 is shortened from SLPS 02000/SLPS 02001/SLPS 02002/SLPS 02003
SLUS-01251/01295-01297 is shortened from SLUS-1251/SLUS-01295/SLUS-01296/SLUS-01297
SLUS-00662/00668/90028 is shortened from SLUS-00662/SLUS-00668/SLUS-90028
ULES 00645 00865 is shortened from ULES 00645/ULES 00865
There is also an argument that
SLUS-00879
SLUS-00900
is one sequence despite being formatted on two separate lines. It appears no different than other items with multi-line formatting styles, as often seen within the Xbox family. In those instances, we treat a line break as a space.
None of the five example items I've presented, by your definition, have "one" item number but are one single item number sequence.
Just like we have a rule that Sony serials must include a hyphen ( - ) when submitted as Item Number field data whether it's present or not, the same sort of guideline can just as easily be enforced with a forward slash ( / ) in these instances of long-chain, multi-part item number sequences specific to the Sony serial itself (therefore not secondary information such as 7063491 from the Metal Gear Solid: Portable Ops / Silent Hill: Origins item) while maintaining the original formatting convention. Such a rule would instead allow these inputs:
SLPS-02000~3
SLUS-01251/01295-01297
SLUS-00662/00668/90028
ULES-00645/00865
SLUS-00879/SLUS-00900 or SLUS-00879 SLUS-00900