May the declaration of biobased or recycled content be based on generic data?

No. 

When a product is made in whole or in part with biobased or recycled materials, the provenience of these materials shall be presented in the EPD as part of the content declaration. In case of recycled materials, it shall include both pre- and post-consumer materials according to the default rules in Section 9.5.4.1 of the GPI, but only post-consumer materials if the applicable PCR says so (see, e.g., PCR 2019:14 Construction products). 

The declared share of biobased/recycled materials shall be based on the actual share of biobased/recycled material in the product (in average over the studied time period, normally 1 year of production). In other words, the share of biobased/recycled materials of, for example, global average production of the constituent materials, for example as stated in generic LCI datasets, shall not be used as the basis for the declaration of biobased/recycled content.

If the share of biobased/recycled materials is unknown, this part of the content declaration can be left out (unless otherwise required by the PCR) or it can be stated to be 0% (a conservative estimate) or unknown.