Postal Employees

My post offices transfer policy is 1 to 6 ratio. My question is I think when they done away with the mail handlers at my office they made a deal to convert some over to mail carriers and part of it was they would have to convert so many from within before they could bring in a transfer. Where would I be able to find the details to such a deal? Also the normal ratio of 1-6, do they have to bring in a transfer or do they just have to make it available to transfers but could still turn them down if someone from within was better fit for the job. And say it’s time to bring in a transfer but no one applies do you have to offer it again the next time around or is the fact that no one wanted to come satisfy that policy and you can go back to converting from within again.