The math is fine. Divide the number of flowing pilots by the number of pilots flowing each month and you have the number of months the last pilot should wait to flow.

Some pilots will leave (resign for greener pastures hopefully) instead of flowing, meaning the number you get here is a bad-case scenario where no one senior to you gets out. However, it is not a worst case scenario. There are lots of worse ones. Here are some plausible scenarios that are worse: AA stops doing classes for awhile. Envoy has to meter the flow to staff the airline - in a situation where attrition is pulling your flow time down significantly, this is very likely in my opinion. Maybe you raise the ire of management somehow and they withhold your flow as an example to the other peasants. A reorganization occurs at Envoy or AA that reduces or eliminates the flow. You can go on forever thinking of these.

I've noticed that a lot of voices here basically just post "actually, that's wrong" or "you left out some important details" to attack others' credibility and never share the "correct math" or the "important details." It makes no difference to me, but the real answer is that no one really knows. Projections have been made based on certain assumptions, and the closer you are to flowing, the more likely reality is to match the projection. That's it. Everything else is a spin job.