Since I did not see any replies, I will add my input on what I would expect companies are doing. I have heard questions like this from others so this may be useful information.
Let's take the case of an update to the REACH Candidate list - example: Dec 2013 update. In this case, the update to the compliance specification adds in the new substances to the list. This is cumulative update so all substances that were previously restricted based on the June 2013 update are included. I would expect customers to deploy the Dec 2013 update and then quickly disable the June 2013 in the application.
For customers that collect IPC Class D or IMDS full material content declarations, there may be a short span of time as the business transitions processes to start using the Dec 2013 list for decision making.
For customers that collect IPC Class A or IPC Class C declarations, there may be a longer time that the older revision of the specifiction (June 2013) remains in use. In this case, there is a period of time where you must recollect data from the suppliers to identify if they are using any of the new substances on the list. The information previously collected for June 2013 is not valid for assigning a Dec 2013 status.
Once the span of time is over I would expect that customers disable the older version of the compliance specification (usually removing the specification from the pickup directory). Just hiding it in the UI still leaves it as an active specification and results in that older version of the specification continuously being calculated. If you leave too many specifications as active but hidden your data size will continue to grow and certain pages will continue to show the old information. I would not recommend using the "set specification applicability" feature for older specifications. If your business has stopped using that version of the specification, disable it.
I know that many customer do deploy the new versions of the compliance specifications as soon as they are available. As soon as updates to regulations are announced we do get a number of requests asking when the updates will be available in our software.