This appears to be correct. This is what I have in my files regarding the Congolese Air Force Mirages :
M201 Mirage VDM to LFBZ in 1989, to Brazil as 4908
M202 Mirage VDM w/o 081278 mid-air collision with M410
M203 Mirage VDM to LFBZ in 1989, to Brazil as 4909
The Miage M201 and M203 were brought back to France in 1989 for undergoing some maintenance, but ,probably because of financial reasons, this job was never completed.
In 1996 the aircraft were bought back by the manufacturer and the aircraft were place in storage at Chateauroux-Déols, France. After that they were converted for the Brazilian Air Force. I have no info on when exactly the aircraft were sold to Brazil, the Scramble database gives a first note date for the 4908 of 1999.