Just called smith. Mine was made in 1998 and the guy told me no plus p.
Yeah, that what the book shows too.
While a +P load will not blow it up, because of the aluminum frame, +P will wear it out faster.
serial number begins 674XXX
SN's ran from 632132 in 1931 to 682419 in 1940.
38/22 Terrier (pre war).
SN's ran from 38976 in 1936 to 54474 in 1940.