Sudden Puncture Repetition

Having enjoyed some 1700 puncture free miles riding the Bolt On Bike on a pair of Schwalbe Delta Cruisers, it came as no real surprise or disappointment that I suffered a puncture a couple of weeks ago.  What has been surprising and extremely frustrating since is the now almost daily occurrence of
punctures.  Despite the fact that the offending tyre appears outwardly  to have some useful life remaining, it's clearly in need of urgent replacement.  You would imagine that a tyre's ability to withstand punctures would decline steadily over a period of time, rather than immediately after a certain reduction in  the thickness of the thread.  I have witnessed this strange characteristic occur on a pair of Schwalble Marathons that I had fitted to my Brompton and can only put it down to the fact that the cause of the punctures are invariably tiny sharks tooth shaped fragments of flint, that get picked up and lay concealed in the tread waiting for that certain point of tread wear where they can work their way through the carcass and innertube.  Although I'm happy enough to replace a cheap tyre like the Delta Cruiser after 1700 miles I do wonder if anyone else has experienced this phenomena of sudden puncture repetition?