iTunes sync/songs purchased by multiple accounts

Interesting. I thought from past experience that family sharing did not work retroactively, only on purchases made after sharing was established. I'll try that. (I still need to get our family accounts shared/linked.)

My exact problem is that iTunes will not download my iPhone's entire library to the new laptop. It refuses to download any songs purchased on my wife's or daughter's accounts. Which I understand ... it's just that was never an issue on previous laptops. I wasn't sure why it suddenly became an issue on this one. (And, as I said, it's not an authorizations issue, because I already addressed that.)

And even then it wouldn't be a big deal -- I still have the entirety of my library on my iPhone -- except iTunes also won't let me upload to my iPhone individual songs. It will only let me sync the entirety of the library on my new laptop. And that's no good because, as I noted before, the library on my laptop is incomplete. So if I sync to that, I'll be losing nearly 80 songs.

But I'll try the family sharing thing and see if that resolves the issue. If you have any other advice beyond that, I'm all ears. Thanks much!

"You need to get all the content you want on your device into the library that you want to manage it with."

Right. And that's my problem ... iTunes on my laptop isn't letting me do that. It won't download from my iPhone any of the songs (about 80) that were purchased by my wife or daughter. Even though that was never a problem on previous computers we owned. That's what I'm trying to figure out.

On previous computers, everything that is currently on my iPhone also was downloaded into my iTunes library on the computer/laptop. We recently had to get a new computer, and now that's suddenly an issue. I can't download from my iPhone onto this laptop/into iTunes any song that was purchased by my wife or daughter. I want to get all the content on my device into my library. iTunes won't let me.

I think I have finally figured out what's going on here. This new laptop will only let me authorize one iTunes account at a time. That wasn't the case in previous computers we had. On those, we could set up different user accounts for the computer, and each account had its unique iTunes account. That's still the case on this new laptop -- we can create separate user accounts for the laptop -- but it's not letting us authorize more than one iTunes account at a time. Frustrating and disappointing. But I think that's the source of my issue.

I should have also noted ... we turned on family sharing too late. So that's not an option for songs already purchased (at least so far as I am aware).