Use keychain to store device ID

I noticed that my ForVendor id is always changing. Someone told me that it doesn't change when downloaded from iTunes. However, I am not sure about this. So, I want to keep the first generated ForVendor id. I found this class, JNKeychain, from one of the posts I checked. It can store password and other data. I tried to use this to store my ForVendor id. Even after uninstalling my app and reinstalling using XCode, I was able to get the value I saved. Sounds good because this way my ForVendor ID can persist regardless of whether it was downloaded from iTunes or not. However, I am not very familiar with Keychain. I didn't even know we could store secure data using it. I read their documentation and it says,that it is usually used to exchange data between applications and your applications must have the same provisioning profile, etc ... I have no plans to share. I just want it to store my ID so it doesn't bother me. My only problem is how long will my data persist in the keychain storage? Will it be deleted after a while? or when do I turn off my device? When do i update ios version? Can it last forever? Will key decoupling have different behavior if I am using a developer / distribution profile?how long will my data persist in keychain storage? Will it be deleted after a while? or when do I turn off my device? When do i update ios version? Can it last forever? Will key decoupling have different behavior if I am using a developer / distribution profile?how long will my data persist in keychain storage? Will it be deleted after a while? or when do I turn off my device? When do i update ios version? Can it last forever? Will key decoupling have different behavior if I am using a developer / distribution profile?