Complex sentence: For modern theatre historians, however, it has contributed to the difficulty of researching theatre from this period in Spain, as the vast majority of plays remain virtually untouched, in terms of both production and scholarly analysis, since the seventeenth century.
Split into simpler sentences: For modern theatre historians, however, it has contributed to the difficulty of researching theatre from this period. The vast majority of plays have remained virtually untouched, in terms of both production and scholarly analysis, since the seventeenth century.