If the MCPS is successful, you will get within the 66. Cause of the 66, 30% (20 flats in this case) allocated to MCPS.
However, when I mean successful, I mean successfully balloted within that 30% allocated to that scheme, and not successful in the sense where HDB acknowledges the MCPS status. Acknowledgment only places you in that first pool, not guarantee you a number. So if there were only 20 MCPS status applications, all 20 will get within the 66 flat in this scenario.
But like that you mention as well, MCPS can get no queue number cause for example in this scenario, if there was 100 who applied with MCPS status, only 20 will be successful in that 30% allocation. The remaining unsuccessful 80 will, as you said, get additional chance, cause they will now join that pool of first timers with no priorities. Which is the last 15% allocation (10 flats), assuming all 50% under the PPS scheme was successfully balloted away. If for example only 10% of the PPS scheme was taken up, then the above 15% allocation will be 55% instead (15% first timer only + 40% remaining of PPS allocation). So once you get into this pool, your schemes all plays no part now, you become a first timer with no scheme. Then if again you’re unsuccessful in this ballot pot. Ta-da! No number at all.