Step One: Keycite or Shepardize to see if the regulation was held unconstitutional or otherwise invalid by a court
Step Two: Find any new regulations changing, adding, or repealing regulations.
In the current Ohio Administrative Code, after the text of the code section, you will see a "history" or "credit" section. Here is a typical example:
History for Ohio Admin. Code 3770:1-2-01 Authority of the [lottery] commission:
The citations in this history section indicate the year and page number of the Ohio Monthly Record (OMR) where you can find prior versions of the regulation. The letters indicate what happened to the regulation, for example, R-E means repealed and reenacted, RRD means the rule review date and A means amended. There is a table of abbreviation meanings in the first volume of the Ohio Administrative Code.
Note that the last citation, "prior OLC 2.1", does not have an "OMR" cite. That is because the regulation was issued before the Ohio Administrative Code was created in 1977. Pre-1977 regulations can be obtained from the agency itself. Area libraries may also have some of these old regulations. The State Library of Ohio (part of Ohiolink) has the most complete collection of pre-1977 regulations.
Places to find prior OAC regulations:
Ohio Monthly Record (OMR)
KFO 35 .A23 O35 (Franklin County Law Library has the OMR from 1981-2000. Contains a rule number table and subject index.
Westlaw - Ohio Historical Regulations
Contains the OAC back to 2002. (If you pull up the Ohio Administrative Code, on the right side, you will see a link to Ohio Historical Regulations. )
Go to Browse Sources to find OH State Net Regulatory Text (text of proposed and final regulations, 2001-.)
Prefilter for Administrative Codes and Regulations, Ohio. Your results will include Regulation Text (text of proposed and final regulations, 2001-.) You can postfilter by for just Regulation Text.
Regulations before 1977
See previous paragraph. Obtain from agency itself, local library, or State Library of Ohio. May be reproduced in older treatises.