So it's all Blacksheep's fault that my extremely accurate issue Omega 'disappeared' into stores when being serviced at Changi
Possibly. If it passed the "Standard Serviceability Test" which consisted of a three position calibration check, then it would not have been opened for internal clean/regulation. I'd just fit a new crystal give it a polish and return it to stores with a nice green label. What happened to it before or afterwards was none of my business. If it failed the incoming test it would have been opened, cleaned and lubricated before being adjusted and released. If it could not be got into calibration limits in all three positions it would normally be sent back to stores with a "Repairable at Depot" (RD) Label to be sent away for repair at an MU. Towards the end at Changi, with the closure of Seletar and 390 MU, anything categorised as "RD" would have been scrapped - and V&A items like Omegas would first be rendered unusable.
I wore a personal Rolex "Daytona" chronograph at the time and did not pay too much attention to the watches that came our way in between all the aircraft instruments. The Rolex died after about 17 years and was replaced with the Omega Seamaster that I wear to this day. I have found my Omega to be far superior to the Rolex.