Can I verify that digital object exists before a given date? It is possible to hash public info (e.g. new york times headline) into an object to verify that it existed after a given date. Is it possible to do the obverse, namely verify that an object must have existed before a given date?
You can do all sorts of verification with a time stamped hash and signed hash, but it can't be a NYT headline. Just as MD5 hashing is now considered insecure and ineffective, the block width of a NYT headline is insufficient. Actually, the input entropy of the textual headline is only a few tens of bits.  "Trump Convicted" does not hold a lot of entropy, which means that another headline at another time might hash to exactly the same value.

You also can't do what all good kidnapper's do and take a photo of the paper's front page alongside your object. This isn't just for the obvious reason that it's digital, but noise and the avalanche effect will ensure that you'll never manage to exactly replicate the image for future verification.

The thing to do is to hash sufficient cohesive public data. Something like the FTSE 250 list of share prices (at the time of hashing and signing) contains enough entropy to make collisions impossible. There's over 8000 bits of pure entropy available there by my calculation. That's sufficient for any possible cryptographic use.  The Million Dollar elliptic curve purports to use public lottery results but that must be  very cumbersome to collate. The music industry uses almost imperceptible fluctuations in the mains frequency to watermark tracks. A frequency vs. time curve could be hashed and keyed alongside the object. Object dating could be achieved for the timespan of available records.

So for example, to check if your object existed at any particular time you'd simply hash and key against all the records you have available. A hash match at a particular time would prove the existence of that object at that time.  You might be able to check with a 15 minute granularity for FTSE250 share prices. Again the most important thing is to hash against sufficient entropy to preclude manufactured collisions. Clearly you can't use this technique if you don't have reliable digital entropy for the time period under consideration.