Does the HMCE tool treat historic damages and expected damages differently?

No. The HMCE tool treats expected damages and historic damages in the same manner to estimate project benefits. However, because expected damages and historic damages are determined differently, there are different rules for their use (described below), and the HMCE tool cannot conduct an analysis based on a combination of expected and historic damages.
Historic damages are based on records from actual past disaster events. Since the recurrence intervals (RIs) of historic damage events may be known or unknown, the HMCE tool is capable of conducting analyses of historic damages with events of known RIs, unknown RIs, or a combination unknown and known RIs. (Refer to the HMCE Tool User Guide for additional details.) Historic damages must be documented based on damage reports, insurance claims, or other historic records.
Expected damages are based on damages predicted from a theoretical model or engineering analysis. For this reason, expected damages tend to be more difficult to justify than historic damages, and unlike historic damage events, the RIs of expected damage events must be known. The HMCE tool is capable of conducting analyses of expected damages with one or more events of known RIs. (Refer to the HMCE Tool User Guide for additional details.) Expected damages must be documented based on complete theoretical damage models, engineering analysis, or applicable historic damages with similar characteristics.