May or may not be something you really want to do - have to think about all long-term consequences - but could approach this way:
In each Product context, add the text to the OIR for EPMDocument as a prefix.
- Have to remember for a new product to create this OIR.
- It won't be "project-generated," just static text.
The numbers will continue to be pulled from a single sequence in the database, so using your example above in sequence this would result:
Designer 1: Create part in Product ABC: 435698-10065.prt
Designer 1: Create drawing in Product ABC: 435698-10066.drw
Designer 2: Create drawing in Product DEF: 738346-10067.drw
Designer 1: Create part in Product ABC: 435698-10068.prt
Seems like this may not be the best situation - all kinds of issues result from using part numbers with "meaning" and trying to accommodate.
Moving sometimes has to be done - the Number & filename would remain.
Renaming would allow the root number to remain but the prefix change or vice versa.