The newer releases are "testing" releases, mostly, where metro is trying them out before updating everyone's PRL.
Remember that PRLs cost them money, since it's a Preferred
Roaming List, so when your phone cannot find metro's towers, it will "borrow" signal from a roaming partner (say VZW, for example). Notice that you may not even
know that is happening, because, depending on the agreement, it might show up as your "home" network still, and not force you to roaming mode. But metro still has to pay the contract partner for using their bandwidth.
The good thing for eveyone else is, while they may update the PRL for a particular region somewhere to improve
their access while they "test" everyone else, the PRL, being national, will include all updates for other areas as well. So we get to see the goodies that they plan on rolling out to all at a later date, the lag being to ensure testing proves the PRL will not actually hinder network connectivity.
Imagine if in trying to improve coverage in say, Las Vegas, they update the whole network's PRL country-wide and it happens to kill coverage in some areas. It would then be a headache to try and get to all those phones so they stop the financial bleeding, by having all of them joining the "extended home" network since the local towers are suddenly unrecognizable.
However, if they roll it out after extensive testing, and assure themselves that all their towers are included in the PRL, they don't have to worry about all that.
(see section 3.2.3 of attached PDF!)
Also keep in mind that the PRL that a particular customer should get would be configured by the operator and could depend on various factors, including device type and subscribed service plan.
Read the attached pdf file for more info.
