I’m flying to Frankfurt next week. As a Velocity Platinum member I get to take an additional 20kg and, after checking with Singapore Airlines, that’s all good for the way there. On the way back I will need to check in at a Lufthansa counter and there the fun begins: Singapore Airlines have no clue, Virgin have no clue and Lufthansa just hung up after I waited about 30 minutes.
Your velocity platinum benefits only applies on travel with Singapore on Singapore or Virgin Australia coded flights. So if you are travelling with Lufthansa, that leg will technically not be eligible for any Platinum benefits.