I have had a bitcoin core wallet on windows for a long time. For most of this time I have been inactive. My client has gone out of sync and my wallet sat on my computer as well as a backup on a usb stick. Recently I decided to get back into crypto, so I re-synced my client to the blockchain. Dropped my old wallet back into the client. It went through the rescan process, and to my surprise I had more bitcoin than my addressees say they have on blockchain.info.

I even decided to dump all my private keys from my core wallet, and import them into an electrum wallet to see what it would yeild. And upon doing so, my electrum wallet has less bitcoin than my core wallet.

How is this possible, considering both wallets are built off the same private keys?