I'm not actually asking about the PSGC codes or the is_in key (you appear to be using them as expected), and the local community has discussed this before, and treat those as "facts".

However, it seems you're saying that you're tracing boundaries from the PSA geodata ?

May I know if you got PSA's permission before doing so? If so, can you share with us the permission letter you got from them?

By any chance, have you encountered this FAQ before: https://osm.org/wiki/Philippines/FAQs_for_PH_data#Frequently_Asked_Questions_about_data_sources_for_OpenStreetMap_contributors_in_the_Philippines