Regarding sending welcome messages, this is what I found. It appears that the member numbers are going in ascending order so the next highest number will be your newest referral. For instance, if you last referral member number is 123456 and your next referral number is 145789 then that one is your newest one.
I only have 5 referrals as of now so it's not hard to keep track. What I plan to do is start a log to keep track of my member's numbers and when I sent a welcome message.
Once I get into the hundreds of referrals (hopefully LOL), I think the log will be quite helpful.
ccbucks