It's not all Tesla owners, just Model S and Model X owners, so the 2nd co-worker won't get ahead in line with another reservation just because they now own an M3. It's also not clear that MS and MX owners still get priority reservations. I've heard conflicting stories on that.
From what I've seen almost all transfers are between MS/MX owners that reserved early on and a friend or family member. Only a handful are being sold I don't think I've seen a single case where someone reserved, transferred, then reserved and tranfered a second time.