Re: Diving into an old BTC wallet from ~2014 and found a nice surprise - what next?
Any attempts to perform a test transaction to move a fraction of that amount show the same "0/unconfirmed, not in memory pool" message that I reported earlier in this thread, with the earlier wallet.dat file.
So with a fully synced Bitcoin Core... and a fully rescanned wallet, it shows a balance but then says "0/unconfirmed, not in memory pool" if you try and send a transaction? 
Or are you getting that if you just open the wallet.dat file and try to send coins? If the latter, then it's likely because the wallet itself isn't "synced"... so you're attempting to send coins which no longer exist... the transaction will be rejected and you'll end up with the "not in memory pool" type error.
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I've run -dumpwallet and swept the keys into a new Electrum wallet, per the process mentioned earlier in this thread, which yielded nothing - just ~140 lines resulting in "no inputs found" in Electrum. (From reading further forum posts around that Electrum message just now, I have not yet tried the -listunspent command in that wallet, so I'll try it once that wallet finished rescanning.)
That would tend to indicate that the wallet is actually empty... and the balances you're seeing when you first open were accurate when the wallet was last used, but the coins have since been spent and therefore, the wallet balance is actually zero.Quote
although one file (created in late 2015) is showing a message when I try to load it which ends: "...wallet is corrupt. Try using the wallet tool bitcoin-wallet to salvage or restoring a backup."
Generally, that doesn't end well 
PyWallet might be able to recover somethingThe old salvagewallet option has been removed from the "core" Bitcoin Core app... so you can't use the -salvagewallet commandline argument with bitcoind or bitcoin-qt anymore... instead, it looks like there is a "bitcoin-wallet" (or "bitcoin-wallet.exe") that is now bundled with Bitcoin Core that you can use and the command is now salvage:
Code:
Bitcoin Core bitcoin-wallet version v0.21.0
bitcoin-wallet is an offline tool for creating and interacting with Bitcoin Core wallet files.
By default bitcoin-wallet will act on wallets in the default mainnet wallet directory in the datadir.
To change the target wallet, use the -datadir, -wallet and -testnet/-regtest arguments.
Usage:
bitcoin-wallet [options] <command>
Options:
-?
Print this help message and exit
-datadir=<dir>
Specify data directory
-wallet=<wallet-name>
Specify wallet name
Debugging/Testing options:
-debug=<category>
Output debugging information (default: 0).
-printtoconsole
Send trace/debug info to console (default: 1 when no -debug is true, 0
otherwise).
Chain selection options:
-chain=<chain>
Use the chain <chain> (default: main). Allowed values: main, test,
signet, regtest
-signet
Use the signet chain. Equivalent to -chain=signet. Note that the network
is defined by the -signetchallenge parameter
-signetchallenge
Blocks must satisfy the given script to be considered valid (only for
signet networks; defaults to the global default signet test
network challenge)
-signetseednode
Specify a seed node for the signet network, in the hostname[:port]
format, e.g. sig.net:1234 (may be used multiple times to specify
multiple seed nodes; defaults to the global default signet test
network seed node(s))
-testnet
Use the test chain. Equivalent to -chain=test.
Commands:
create
Create new wallet file
info
Get wallet info
salvage
Attempt to recover private keys from a corrupt wallet. Warning:
'salvage' is experimental.
bitcoin-wallet is an offline tool for creating and interacting with Bitcoin Core wallet files.
By default bitcoin-wallet will act on wallets in the default mainnet wallet directory in the datadir.
To change the target wallet, use the -datadir, -wallet and -testnet/-regtest arguments.
Usage:
bitcoin-wallet [options] <command>
Options:
-?
Print this help message and exit
-datadir=<dir>
Specify data directory
-wallet=<wallet-name>
Specify wallet name
Debugging/Testing options:
-debug=<category>
Output debugging information (default: 0).
-printtoconsole
Send trace/debug info to console (default: 1 when no -debug is true, 0
otherwise).
Chain selection options:
-chain=<chain>
Use the chain <chain> (default: main). Allowed values: main, test,
signet, regtest
-signet
Use the signet chain. Equivalent to -chain=signet. Note that the network
is defined by the -signetchallenge parameter
-signetchallenge
Blocks must satisfy the given script to be considered valid (only for
signet networks; defaults to the global default signet test
network challenge)
-signetseednode
Specify a seed node for the signet network, in the hostname[:port]
format, e.g. sig.net:1234 (may be used multiple times to specify
multiple seed nodes; defaults to the global default signet test
network seed node(s))
-testnet
Use the test chain. Equivalent to -chain=test.
Commands:
create
Create new wallet file
info
Get wallet info
salvage
Attempt to recover private keys from a corrupt wallet. Warning:
'salvage' is experimental.