How to ensure first RPDO arrived

I noticed that when I launch my application, comprising an AsyncMaster + 16 instances of LoopDrivers (so 16 slaves), some RPDOs have not yet been received. If I read them without waiting a bit, I get garbage.

Is there a way to wait for the first RPDO message has arrived from each slave? I mean, after issuing master->Command(lely::canopen::NmtCommand::START), is there a way to wait until all RPDOs have been collected 1 time, so that no garbage is read from rpdo_mapped?