Same CRS Different EPSG

[CheFusi]

CRS Transformations

st_crs(DEM_NAD83) == st_crs(SFtracts_NAD83)

is true because the CRS' are both NAD83, but the former has EPSG",9122 and the latter "EPSG",4269.

So the workaround:
DEM_NAD83 = projectRaster(DEM, projectExtent(DEM, st_crs(SFtracts_NAD83)$proj4string))

works, but it's a bit confusing because the alternative way of reprojecting is inputing the EPSG. So it could be useful to clarify this difference in CRS and EPSG