Solution : https://service.sap.com/sap/support/notes/374087 (SAP Service marketplace login required)
Key words : 
symptom db02 missing index analysis shows missing 0-indexes, prerequisites missing functionality solution apply bw 2, infocube fact tables, terms dbdiff db6, infocubes db02, unknown indexes, display errors, created correctly, report   sap_update_dbdiffdb02, longer show
Related Notes : 
       
| 414728 | SAPBWNews BW 2.1C Support Package 12 | 
| 374502 | DB6: DB2 UDB - BW Performance - Overview of notes | 
| 328322 | DB6: DB2 UDB EEE Indexing Scheme of BW Facttables |