My guess is JFRV is a "R"esident "V"isa for the purpose of "J"oin "F"amily. It is just a permission to enter Taiwan, and valid for no longer than 3 months. IMO, it should be distinguished from ARC.
Information on Republic of China Resident Visas
Foreign nationals, who hold ordinary passports or other legal travel documents, who intend to stay in the Republic of China for more than six months for the purpose of join family; pursed studies; undertake employment; invest; conduct missionary work; conduct official duties; participate in international exchange programs; and engage in other activities approved by MOFA or other relevant agencies at the central-government level.
A Resident Visa is valid for three months.
Duration of stay:
Resident Visa holders are required to apply for the Alien Resident Certificate and Re-entry Permit at local service centers of the National Immigration Agency within 15 days starting from the next day of their arrival. They may stay in the ROC as long as the Alien Resident Certificate remains valid.
The page also says,
6. Those who enter the R.O.C. (Taiwan) on a Resident Visa or get a Resident Visa after having arrived in the R.O.C. (Taiwan) must apply for an Alien Resident Certificate and Re-entry Permit at local service centers of National Immigration Agency. The former must apply within 15 days from the next day of arrival, and the latter must apply within 15 days from the Resident Visa issuance date. Duration of stay is noted on the Alien Resident Certificate.