In the older posts, there is a link to the pdf file "dse_ric_structures.pdf" but unfortunately the link is not valid anymore.
Believe this document was obsoleted and is not available anymore.
The general guidance can be found on My Refinitiv Use of Reuters Instrument Codes (RICs)
Additionally, if you are looking for rules on specific instrument type, you may find it via search on My Refinitiv, for example:
If you have access to Refinitiv Real Time, a very useful resource is RIC = RULES1 (Speed Guide). From it you can navigate to all the current rules on RIC structure.
RIC search tool is available to developers via RUC Search
As a customer, if you can not find what you are looking for within Refinitiv content, please contact Refinitiv content experts via Refinitiv Helpdesk Online -> Content
Hope that this information will enable you to proceed on your requirements.