John, first supply is certainly documented, from which first operational use is implied. TW Supplies Dept weekly report for week ending 1 July 1916: "Of the preliminary order for 200,000 special base plugs and rods, 25,000 were despatched to France, and it is expected that about 40,000 will be despatched next week."
Deliveries continued slowly but steadily throughout July; allowing for training with the new store and delivery to the lines of communication, it is likely that the No.23 first saw action from the middle of the month. At that time things were of course a little sticky on the Somme front, so there was probably some urgency in seeing it introduced.
Tom.