Complex sentence: It is impractical, therefore, to limit a description of the records of the subcommittee to those through 1968, and although the files were begun in 1951, some contain data that precedes the creation of the subcommittee.
Split into simpler sentences: It is impractical, therefore, to limit a description of the records of the subcommittee to those through 1968. And although the files were begun in 1951, some contain data that precedes the creation of the subcommittee.