After the seismic loading condition of existing building is changed, to evaluate existing building, determine the design objective and seismic load, engineers have to collect the as-built information and field verify existing building characteristics. No as-built information, seismic retrofit calculation is impossible, only prescriptive seismic retrofit design is possible. The existing building SFRS ductility level may be found from the old drawings, design notes etc. of existing building. If ductility level is not addressed clearly in old drawings, a try-and-error calculation and detail review may help you to figure it out. Typically very old existing buildings were designed with low ductility, assuming them belong to conventional construction may be acceptable. , i.e. RdR0=1.5*1.3=2(timber structure is excepted.) , nevertheless, engineer review to verify ductility level can not be omitted. When a new SFRS is added to an existing SFRS, according to the code, for combinations of different types of SFRS acting in the same direction in the same storey, RdRo shall be taken as the lowest value of RdRo corresponding to these systems, therefore, the RdRo of new added SFRS shall be equal to or lower than that of existing SFRS. After retrofit solution is incorporated, where a building is altered,rehabilitated,renovated or repaired, or there is a change in occupancy, the level of life safety and building performance shall not be decreased below a level that already exist(NBC 1.1.1.2).

Refer to answer of Question 1