Many thanks, Rick, for picking up this delicate topic and for the links to related articles.

Regarding Chris Hemedinger's blog post "Pitfalls of the LAG function" (2012): In a 2018 discussion in the SAS Support Communities evidence was presented that the behavior of the LAG function described in that post can be explained without assuming Boolean short circuiting and that the results would have been different had short circuiting occurred: https://communities.sas.com/t5/SAS-Programming/If-statement-Short-circuiting-and-Lag-function/m-p/473693 and https://communities.sas.com/t5/SAS-Programming/If-statement-Short-circuiting-and-Lag-function/m-p/473832. This would be consistent with Polzin's statement about side effects preventing short circuiting.