The truth of the matter is that like many things in Ryanair, the answer is "there is no answer". Date of joining etc etc which have some bearing in "traditional" airlines counts for nada in RYR. One guy can finish, request a base , and wait 2years to get there. Another guy can finish his line training somewhere, like it, and end up being allowed to stay, why, nobody knows. With the previous guy who did base allocation the system seemed to be (allegedly) roughly aligned with how many bottles of wine you dropped in, the current one is feared to make these choices (allegedly) depending on what side of bed he got out of that morning.
Anyway welcome to the "Alice in Wonderland" world of Ryanair, where very little is quite what it first appears to be.