Receiving "The results of this report are too large. Please narrow your results." but data

I have a client who wants to see reporting for a rolling 24 periods.  I can only see a way to get a rolling 18 periods easily.  To compensate, I added two amounts columns, each showing a rolling 18 periods.  One is based on report date, one is based on current date.  The result is that I get 36 months' worth of financial data in addition to other columns on the report.  The message in the topic title also comes up.

Is this message saying that the report is missing data?  There's some data in all columns, but I obviously don't know if it's completely accurate without spending a lot of time tying it out.  I found an old thread mentioning that the cap on reports is around 75,000 lines; has that been increased?  This report, when exported is about 74,500 lines so it's nearing the limit if that still applies.