As scan compression becomes ubiquitous, ever more complex designs require higher compression. This paper presents a novel, two-level compression system for scan input data generated by deterministic test generation. First, load care bits and X-control input data are encoded into PRPG seeds; next, seeds are selectively shared for further compression. The latter exploits the hierarchical nature of large designs with tens or hundreds of PRPGs. The system comprises a new architecture, which includes a simple instruction-decode unit, and new algorithms embedded into ATPG. Results on large industrial designs demonstrate significant data and cycle compression increases while maintaining test coverage and performance.