Totally naive to COBOL here, why do you have to do it? You said you wrote some regexes for the pull and transform, why not pipe the source to a program that finds that period for you?
I'm not sure how and on which machines COBOL code is written and compiled these days but I reckon that piping it to grep, or similar tools, might simply not be an option on those machines.
Here's someone asking about doing just that:
https://serverfault.com/questions/356574/can-i-run-grep-agai...
[0] https://en.wikipedia.org/wiki/MVS#MVS/XA
(Edited to go back even further than OS/390)
The problem isn't finding the destination, its what alternately happened been source and destination.
Also, if your reading on paper, CTRL-F isn't available. You're scanning those pages by hand. When you're sitting there, highlighter and pen in hand to make annotations and point out important shit, its a problem. End up with circles around the periods and arrows point to it with comments like "this is how we got to x from y."
Edit: also if you end up at the same place regardless of the source or from multiple sources. You can't keep the code for a level to find everywhere a jump emds up there.
"sentence".capitalize()