runManifestDemo.sh was reworked in April of 2017 to accept a single --tag parameter that it attempts to match against a git ref specifically to enable end-users to be able to run the demo against official releases. This would need to be extended to support multiple refs to be really useful under the current CI workflow. However, this would not solve the problem of being able to select the correct version of the demo to run with arbitrary EUPS tags. Eg., w_2018_13 There have been several discussion on slack about this problem but I don't believe any of them were captured in jira. The current state of affairs means that past nightly/weekly releases can not be reliably rebuilt under CI with the demo enabled. Gabriele Comoretto was bitten overnight by changes to the stack+demo 2 days ago breaking the demo master branch against the EUPS v15_0_rc3 tag.
My position is that the demo should be turned into an eups product, and added to lsst_apps, so that the correct version will be recorded under an eups tag. This would also allow end users that have performed an eups distrib install -t v42 lsst_apps to run the demo as something like setup lsst_demo; lsst_demo rather than needing to document a per release incantation.