You do not get 2 unlocks every month. You can have a maximum of 2 extra unlocks. Every month on the first of the month, you will recieve 1 unlock until you have the maximum of 2.
For example, the first week of January, I reinstalled Windows 98 and unlocked LFS. A week later decided to try Win XP again, installed and unlocked LFS again. That left me with 0 unlocks. Then on February 1st, I recieved an additional unlock to bring my total to 1. Now in March I will recieve another and will have 2 and will only have 2 from there on unless I reunlock LFS and use one up.