Wookey AFAIAA it has never been referred to in the plural apart from the non pilot origin PI stuff and here. Flaps and slats are referred to in the plural because there are usually more than one section of each on each wing, but there was only one section of droop. On most types, the call is Flap 1,5,30 etc. I.e. in the singular.
Based on my experience of over 6000 sectors and around 10,000 hours flying Tridents of all types plus over 100 simulator sessions and being involved on the technical side as well; I'm here to tell you, it's droop not droops.