Thanks for this insight. I checked in the documentation (SAS 9.4 M5) for the data step, do iterative. Indeed, by careful reading it is possible to deduce this syntax but it is not easy. May I suggest improving the documentation of this. Describe it formally, give it a name, as you have done, and refer to it from elsewhere in the documentation. It belongs as a component in "Language reference: concepts > SAS system concepts". Look at any documentation for a SQL database product (not SAS) to see what I mean.

The data step documentation mentions in an informal way the use of WHILE and UNTIL with iterative loops. Do these work in the contexts you describe? The documentation should be revised to make this unambiguously clear.

SAS is particularly in need of clear documentation as it does not have a small well-defined language grammar. Without good documentation for text-based languages all we can do is guess or experiment - or wait for you to blog about it.