I have a special situation, and I'm hoping someone can help me out...
A while ago, when BTC1 was worth maybe $10, I started setting up "cold storage" for my bitcoins. In my ineptitude, I started by installing Bitcoin-QT on a virgin PC that had never been, and would never be, connected to the internet. I then generated an address to which to send some coins (I think I can safely reveal the address: 15dgcomA9Fv9Ecna5T2cNxXpsMnH6wCXmh), and sent a mere BTC3.1052 to it from another (connected) PC. However, since the receiving PC was never loaded with the blockchain nor connected to the internet, it never learned about the coins sent to it (of course, I backed up the wallet). Now, I have a working setup that uses Bitcoin Armory on the isolated PC, and Bitcoin Armory loaded with a read-only wallet on the connected PC (which is piggybacked on Bitcoin-QT, as per the setup instructions). Now, in order to retrieve the BTC3.1052, I loaded the wallet I had backed up, onto another copy of Bitcoin-QT, which was loaded onto yet a third PC that had an up-to-date copy of the blockchain already loaded. Although this copy of Bitcoin-QT is aware of the address that had been earlier generated, and thus presumably is able to receive the bitcoins and then spend them, it does not have knowledge of the BTC3.1052, but instead reports a zero balance.
I have the sender's 64-hex-digit transaction ID, if that helps.
How can I fix this situation? Those coins are getting valuable!