Only if you disregard the amount of latitude that the semantics of these headers give to UAs that would effectively thwart this method of tracking.
If I fetch your /foo.html today in November 2022, and you send me a last-modified from 1978, that gives me and my UA a huge range from which to select a different datetime (anywhere between the 1978 value and now-ish) on my next request. How are you going to correlate my original and subsequent requests if in the latter I ask if you've got a copy that's been modified since 1999?
If I fetch your /foo.html today in November 2022, and you send me a last-modified from 1978, that gives me and my UA a huge range from which to select a different datetime (anywhere between the 1978 value and now-ish) on my next request. How are you going to correlate my original and subsequent requests if in the latter I ask if you've got a copy that's been modified since 1999?