@dguild hi there! how many states do you typically do work in?  When i was an end user, the company i worked for was nationwide so managing all the lien law dates, when to initially file, etc. was hard to track so they used a company called Level Set. 

on the flip side, if you wanted to stay within acumatica, i would think you would need some sort of indicator on the project (maybe just the project address is enough) to specify which state it would fall in.  then I would have a GI for each state or maybe a combination of states if the “file within days” are the same (in your example you used 90 days).  you could bring in the AR invoice and as conditions specify you want only open status documents to come in and it’s 80 days overdue for the invoice date or due date.  from there, you should be able to set up a business event to trigger an email with the list of projects that are approaching the lien expiration date