Hey Vince, 

Due to the geographic isolation that comes with being an archipelago addr:country in the Philippines can be derived from boundaries with 100% accuracy. But I haven't considered the use case mentioned by you. I won't remove the tag anymore from now on.

Regarding addr:province, adding this tag seems to be standard practice in independent cities. While Baguio is administered independently isn't it still considered to be geographically located within Benguet? It is very common for official forms to have a mandatory field for province when asking for an address. What do you enter in those cases? 

Moving on to addr:barangay, I'm not sure why this would be non-valid. It has been in local use much longer (since 2014) and has almost double the usage compared to addr:quarter. It is also used by more different mappers and it's more widespread geographically (25% of addr:quarter usage is in Baguio alone). On the data consumer side Nominatim treats both tags as equally valid and most other applications ignore both. Do you know any platform that only processes addr:quarter, but not addr:barangay?

But now to the practical side of things. Postal addresses are a topic entirely independent from OSM place tag assignment. Seav's LGU proposal is exclusively about the latter, he does not mention addresses at all. Just look at how addr:city is globally established for usage with whatever place name goes together with a postal code, regardless if it's mapped as place=city/town/village/suburb in OSM. Another example is how locally in the Philippines we use addr:province despite provinces being mapped as place=state.

Deviating from this practice of using a single tag for a specific address component leads to multiple problems and complications. To start with, only a small part of barangays (small to medium sized urban ones) are place=quarter in OSM. Most are tagged as village, fewer as suburb and some even as neighborhood, hamlet or town. It's also not unusual that mappers change place tags of a barangay without updating all addresses referring to that place. And it then gets even more confusing considering that quarter is also commonly used for large puroks, sitios and other non-administrative places encompassing several smaller neighbourhoods. Because of this a data consumer that wants to know the barangay of an address currently needs to make wild guesses wether it's found in addr:quarter, addr:village, addr:suburb or if it's missing altogether. And for mappers it's a mess too, many seem to just omit the barangay and only add addr:street/city/postcode.

Addr:barangay avoids all these issues by being very clear and unambiguous. An added advantage is that new mappers will immediately understand this tag and are therefore more likely to intuitively start using it.