I have 2 iPhones among my devices in iTunes. I need to deauthorize the correct one. Help!

Question

My old standby Mac for sync-ing my iTunes library and my iPhone 4 was my G4 Mirror Doors PowerMac. The startup hard disk on that Mac crapped out last month, and my other option for keeping my iTunes & iPhone ecosystem up-to-date -- my MacBook 2.0 GHz -- has problems with its USB ports. SO, now I have pressed into action an eMac with a 1.25 GHz G4 processor, and with all the other requirements (iTunes, Safari, iOS 10.5.8, etc) for sync-ing my new (Jan '13) iPhone 4S.
I did my first sync today between the iPhone 4S and the eMac, via USB hardwire and iTunes. I wanted to load up my phone with music purchases from iCloud, but felt the fastest way to do that would be to first pull all my purchases down into the eMac from iCloud, via My Previous Purchases in iTunes.  Once I entered my iTunes account info (via my Apple ID), iTunes showed me logged in. But I could not drag any music over to eMac from the 10 or so songs I have on my iPhone after downloading them from iCloud to several days ago.
I realized I had to authorize the eMac for my account. Checked the Manage Account > Manage Devices area in the iTunes Store, and it informed my that I had already used my 5 "computers" on my acccount, and two of them are iPhones. There is no information that tells me which iPhone is which, like a MAC address or EAN or serial #. One of them is probably the iPhone 4 that I just traded up from, but which I still have. The other iPhone entry shows "Associated December 28, 2012" in the listing of devices. That date matches the date I set up iCloud on my new iPhone 4S, so it should be saying that my new phone is among the 5 devices already authorized. So I just deleted the older iPhone listing,and now I have 4 devices. I just went to add in the Emac, and iTunes tells me I still have "5 computers" authorized on my account (and therefore still cannot add the eMac).
Are "devices" the same as "computers" in the eyes of iTunes DRM?
Is there a lag time in the iTunes database updating the fact that I deauthorized the (older) iPhone?

Answer 1

The title of my initial post is a bit misleading. I already took a chance deleting one of the iPhones, hoping if I deleted the wrong one, I can still reauthorize it (all with the same Apple ID acct, so not subject to 90-day waiting period, right?) The iTunes database just updated itself, and it says I have 4 "devices" "in the Cloud", but 5 "computers" associated w my account. How can I find out what computers are associated? Isn't there a list I can see? I dont have a clue what computers they might be. If I use the  "Deauthorize All" option, is it a pain to add them all back in. I assume I would have to log in from each computer to reauthorize each one. Would I have to be running the newest OS or version of iTunes to reauthorize? I think I have a PowerBook G4 Titanium with an older OS and iTunes. I'd like to keep that authorized, if possible.