Dear Graeme Fitzpatrick. 
First of all, thank you for your comments.
My name is Thang Quach, GIS team lead from Sovereign Solutions, and  sovereign_khoipm is one of my team member. We are now working on a project of Updating OSM road for several States in India, including 
1. KERALA, 2. TAMIL_NADU, 3. Andhra Pradesh, 4. TELANGANA, 5. KARNATAKA, etc. 
Regarding your comments, in our updating guideline, we use official and reliable sources hosted as xyz tile services, used as a custom background when editing on OSM, keeping in mind that preventing  touching existing buildings as much as possible. 
We will recheck all changesets that have conflicts between our new roads and existing buildings. However, there are cases that the existing buildings are not digitized at correct location and we have no choice but accept crossing some buildings b/c we are now focusing on updating roads, not buildings, and hoping someone will correct the building in the future.
Finally, thank you for your comments, and I hope that we have more discussions when running this project
