I recieved some GIS parcel data a little over a year ago. This data is the basis for the majority of my work. About a week ago I noticed that the Projected Coordinate System had somehow been converted from NAD_1983_StatePlane_Massachusetts_Mainland_FIPS_2011_Feet into WGS_1984_Web_Mercator_Auxiliary_Sphere. I am not sure when this conversion happened as I have not needed to measure any parcels for quite some time. I noticed the change when I went to compare some of our assessing records against the GIS data and they were VERY different from one another. I have projected the data back into NAD_1983_StatePlane_Massachusetts_Mainland_FIPS_2011_Feet and the Shape_Area is now very close to the original data (I kept a backup copy of the original data on a disc) but is still short from the original by about 55 SF for the parcel I checked. Not sure if I missed something but, if anybody can help me to get the Shape_Area of these parcels to match the original data I would be very grateful.
Note - a few parcels have been changed from the original data so I cannot simply reload it. Also the to project my data back to its original Projected Coordinate System i went into ArcToolbox -> Data Management tools -> Projections & Transformations -> Project. Lastly, I'm using ArcGIS 10.2.2 and the file I'm working with a File Geodatabase Feature Class.
I wasn't sure whether to start a new thread for this or, attach add it to one of the many threads about coordinate systems that are already on here. I felt as though this is different from most of the questions on coordinate systems that I have seen on here, so I made the decision to open a new thread.