That is a valid question:

 I spoke with Tom Brady awhile back and asked him the same question about rig number 3. 

He said that there are many rigs who cannot/will not drill in the winter.   This will indeed free up some crews.  We may not see a crew for rig #4 till then?  Keep in mind the last crew came from Mongolia!  There is no stone left unturned to find a crew.  Falcon drilling has an excellent working relationship with TTM and between all parties involved I am confident a 4th crew will be found. 

Tom also said there is manpower to get everthing in place so when the new crew (this was crew number 3) they could commence drilling immediately.

BBOB