It's unlikely he has a hidden stash that is truly hidden. Back then the government wasn't all over the blockchain (compared to today) and obfuscation was not like what is available today.

So even if he does have a stash, it is likely marked, and he will get a knock on the door real fast if it starts moving.

I'm no blockchain forensics...icist, but coins were moved from let's say one main Silk Road wallet to many other people's wallets legitimately, or as legit as a illicit drug transaction can be. Silk Road wallet A transfers coins to rando person's wallet B. Also, wallet A occasionally transfers to wallet F which he owns. Who's to say which wallets he controls?

One of the possible ways Ulbricht got caught was a single Google Captcha that showed his IP address (San Francisco, go figure). So he covered his tracks pretty well.

Coins that have a short connection to silk road transactions and have sat still for the last 12 years.

This would likely be hundreds or thousands of bitcoin, as they were worth ~$50 when he was jailed.

I'm pretty sure there were tumblers back then. Alternately, there's the old "bury some gold under a family member's garden" trick.

there weren't good tumblers back then. and monero didn't exist yet, although a cryptonote implementation did