Tom Roush talks VLFs, changes in DBCC LOGINFO, and Availability Groups:
Turns out SQL 2008R2 (where the original script worked) returns different fields than 2012 and 2014 (where it didn’t).
I figured I didn’t want to find out which version of the script to use every time I needed to run it on a server, so I told the script to figure that out by itself, and then run the appropriate hunk of code (example below)
This is a good explanation of how to back out of a complex situation.