... that to participate in the balloting process for TAPPI Standards you must sign up for the Standard-Specific Interest Groups (SSIGs)? Drafts are available for anyone to review, but to vote and comment you must be a member of the SSIG.

Every Standard has its own SSIG, meaning you must register separately for each Standard you're interested in. You can access links to all the SSIGs organized by subject category on the Join SSIGs webpage for Standards. Selecting the Subject Category if interest will lead you to the corresponding SSIGs to participate in.