How to link particles to target by custom float?

[Alexx31]

Custom float should be set to Birth ID, and make sure your Birth Objects event is evaluating before the other particles are looking for it (right click menu had option to display evaluation order, and you can define that order by clicking an event and changing its evaluation priority).

Aaah, this is why evaluation order is there.
So I can set the important targeted Birth ID to evaluation order "1" and everything else to evaluation order "2" 
and then I get always the same Birth IDs whatever happens later.

Thanks