Early telescopic sunspot observations provide unique information extending our knowledge on
solar activity back to the seventeenth century. In our work, we analyse sunspot parameters reconstructed from
observations in the 1610s. Comparing distributions of historical and modern sunspot group areas, the fraction of
small sunspots apparently missing in historic drawings was estimated. We suggest that reports might lack from 20
to 85% of sunspot groups depending on the style of observations. The number of sunspot groups corrected for the
fraction of lost spots indicates that the period of 1612–1613 apparently belongs to a cycle of a secular maximum.