Simplify the following text for a Grade 7 native English-speaking person.
Original: From here , Microsoft issued three release candidates between July and November 1999 , and finally released the operating system to partners on 12 December 1999 .
Simplified: Microsoft further issued three more test versions from between July to November 1999 . They then finally released Windows 2000 to partners on December 12 , 1999 .