The system works like this:
Every time you buy VIP+ it adds one crate to your crate and 30 days to your time.
If at any time your start time plus your running time is less then the current time, it will expire you.
Each month, I roll the crates and if you have more then one crate in your balance, it gives you one ingame and removes one from the total.
If you have been given a crate and you buy VIP+ it just adds it to your total instead of giving it agian.
This is why when you buy for 1 month, you get 30 days of time and 1 crate.
TD;DR: only 1 crate.