Hi,
First of all I need to say "take more attention"

ANY invite you sent from your account has a limit for its period, after that it will expire and turned into "nonsense"

I am gonna today to introduce a piece of info
if you are about to invite someone to a tracker, you need to tell him to use it before its expiration

tracker staff observing who had invited through account

for example if you send someone invite from a Chinese tracker and it didn`t be used it will turned into nothing and you need to contact staff to get it back

like this,https://imgur.com/R2D6vnV
you can see no invitation with this account despite account owner send it and user didn`t use