Replace case fans, believable specs?

[AuroraProject]

I want to upgrade the case fans in my Lian Li. The factory fans are ADDAs, 2-80mm rated at 26cfm@15db and 2-120mm rated at 72cfm@34db per ADDA spec sheet. Now I'm no scientist, but I'm fairly certain these 120's are not putting 72cfm out. If I was to buy replacements to go quiet, what kind of airflow should I look for? I've found many quiet 120's but they are rated at ~40cfm. Is there any way to gauge what cfm these ADDAs are really putting out?