According to this thread, that's not true.
Do you know how to calculate the gas needed to get yourself & buddy to the surface? You mean 500 psi right? 🤣
scubaboard.com
Many of the "knowledgeable regulars" have stated that there is no specific depth limitation regardless of the level of certification up to the 130' recreational limit.
The joy of legalese versus popular interpretation of that differing, in a self-regulated industry.
The recreational depth limit is accepted and referenced by e.g. PADI as 40m/130ft.
PADI OW e-learning states only that that "Certification
shows that you met the course requirements. .... As a PADI Open Water Diver, you will be trained to a maximum depth of 18 metres/60 feet (or the actual depth you reached, if shallower). You’ll also be qualified to dive in conditions as good as, or better than, those in which you trained ..." (bold mine)
That's all it says. You are trained to whatever depth you reached in your course, and is qualified to dive with a buddy similiarly trained to the same conditions that you were trained in. How many OW instructor out there are able and take their students to exactly 18m?
Similarly in in PADI AOW e-learning, it states that "Although 40 metres/130 feet is the maximum depth for recreational diving (ideally, with certification as a PADI Deep Diver), 30 metres/100 feet is the
recommended limit for Advanced Open Water Divers ..." (bold mine)
Nowhere in their courses do they say "you are certified to dive to X depth". (They may say it in their blog but that's a different story.) Out in the world, it is accepted, including by insurer's terms & conditions, government (e.g. Malta's law on independent [not with an instructor] diving) etc. that equate OW as certified to 18m/60ft, AOW equiv as 30m/100ft and Deep speciality as 40m/130ft.
Say someone is AOW and in a diving accident and need to claim insurance whose T&Cs states only covers to the depth limit of their certification, I wouldn't want to be them arguing I am still within the recreational depth limit when the insurer deny coverage because they went to 31m.