Finding grandparents' lost TW ID

Hi, I’m an NWOHR due to my dad being an NWOHR as well. I want to obtain TW citizenship but we are unable to provide documents claiming my grandfather’s TW citizenship. Are there any other ways for us to check for his ID number?
He is already deceased and we lost track of his passport. My dad can’t remember their previous address as well in Taiwan so it’s kinda hard for me not knowing where to start looking. Are there any centralized agency in Taiwan for the registries?

Does your dad still have any ROC documents, like NWOHR passport?

Yes, he has an active nwohr passport

Best shot would be taking that to any household registration office in Taiwan (ideally one close to where he used to live) and getting more information from them. Are you sure your dad is NWOHR? If his father was an ROC citizen too and he lived in Taiwan before, how come he is NWOHR? Are you sure his household registration isn’t just “moved out”? You can check this by looking inside his passport and seeing if there is an ID number section.

My dad’s passport doesn’t have an ID number as he did not stay in Taiwan very long. My grandfather had an ID number because he took the investment route. Do you perhaps know if the household registry would require any other documents for them to check?

Oh your grandfather was naturalized? I didn’t know that was even a thing that long ago

Yes, he was

Then I guess your dad must have been born before his dad gained household registration or maybe just before he naturalized, otherwise your dad would have household registration too.

Yes, that’s right. Would’ve been a whole lot easier if the timeline was reversed
Any suggestions on what documents I could bring to the registry on my trip to TW?

Doesn’t your father know his fathers name in Chinese at least?

Anyway you cannot get citizenship through your grandfather. So do you have other relatives in Taiwan? Fathers brothers sisters?

You may need to get a TARC and live here before getting HHR and ID card. What other citizenships do you have if any? If you get the new biometric passport you can now enter without a visa. But that’s not residency rights.

He has a passport so it will be in there

He does. Do you think that will suffice?

I would call the Department of Household Registration first to get some info before flying here, but obviously bring everything relating to you, your dad and your grandad that you have.

Thanks a lot @meishijia, I’ll try that

My grandsons can have NWOHR as I naturalized decades ago. It’s been available for a long long time.

I just presumed we were talking about the 50s or 60s when OP said grandfather.

It’s a start. Date of birth and name in Chinese and would help. However as I said you cannot get HHR and ID through a grandparent. My grandsons cannot they have to move here first and live on a TARC for a period of time to get HHR and ID card…

I too naturalized.

Showing my age lol Could be 70’s or 80’s