I have owned a number of die cast "K0"s over the years with VIN numbers 1008621, 1010xxx, 1015xxx, ALL of which WERE fitted with wrinkle tanks. Yet I have a sandcast 1005192 (owned 20 years now) which despite being appearing to be very original did not have a wrinkle tank fitted when found. We have to remember that these things have a lot of history now, often unknown to current owners, so what is correct can be open to speculation / interpretation.
Personally, I believe all sandcasts would have left the factory with wrinkle tanks, and based on observations of original UK bikes, I believe that wrinkle tanks were fitted to most '69 built die cast bikes also, certainly as far as the above mentioned 1015xxx. Just my "thoughts".
Cheers - Chris R.