Except that it is signed as CA-210 east of CA-57 and thus naming it as I-210 produces incorrect driving directions for entering the highway from local streets.
In addition, FHWA (the Federal Highway Administration, part of the US Department of Transportation, the administering authority for Interstate highways) denies I-210 existing in the San Bernadino metro area as per http://www.fhwa.dot.gov/reports/routefinder/table4.htm
and states that I-210 in California is 48.72 miles long at http://www.fhwa.dot.gov/reports/routefinder/table3.htm
, which corresponds to the distance between Sylmar, CA and San Dimas, CA along I-210.
I would suggest that the highway be renamed as State Rte 210 east of State Rte 57 with alternate names added for the Interstate designator if desired.