There's no such thing as an "EB2" PERM or an "EB3" PERM.
At the I-140 stage, USCIS determines whether the PERM satisfies the minimum requirements for the EB category requested in the I-140 application.
Any PERM that satisfies the minimum EB2 requirements of "an advanced degree or bachelors plus 5 years progressive experience" will automatically satisfy the minimum EB3 requirements of "a bachelors degree or 2 years experience required".
A PERM doesn't expire, as long as it is used to support an I-140 application within 180 days of certification. Once that condition is satisfied, it can be used to support further I-140 applications, unless revoked by USCIS for cause.