When DID the Nightstalkers and Cazadores escape?

So we know that Nightstalkers and Cazadores were created by and in Big MT at an unknown date (Dr.Borous says the Cazadores were created around 2002 I believe but seeing as how that's over 70 years before the Great War and the fact that the Think Tank have had their minds tampered with and were already mentally unstable, I think we can rule that out as being true. However we find entire COLONIES of both species in the Mojave, with the Cazadors themselves having even spread to other states and areas like Zion, implying that either they just reproduce and expand at an ALARMING rate, or they've been escaped for quite awhile now.