It’s not just the latex part of the industry that doesn’t have standardized firmness ratings. There are no “standard” definitions or consensus of opinions for firmness ratings in the whole industry and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that feels firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here) so different people can also have very different opinions on how two mattresses compare in terms of firmness. This is all relative and very subjective and is as much an art as a science.
I would also keep in mind that ILD is only one of several variables or “specs” that will determine how soft or firm an individual layer or a mattress “as a whole” will feel to different people (see post #4 here). In addition to this the ILD of different materials or different types and blends of latex also aren’t always directly comparable to each other (see post #6 here) so using the ILD of a particular layer or combination of layers as a reliable indication of how firm a mattress may feel to you compared to another mattress with a different combination of layers can sometimes be more misleading than helpful.
Some manufacturers that make molded 100% natural Dunlop don’t test their cores for ILD and use density as a firmness rating instead and using density may be a more reliable way to approximate the firmness of one 100% natural Dunlop layer vs another (assuming they are both 100% natural Dunlop made in a mold and are the same thickness). The “word ratings” they use aren’t nearly as important as the actual firmness of the layers they have available.
You can get a sense of how the density of 100% natural Dunlop made by Latex Green relates to ILD in post #2 here and other manufacturers would be in a similar range although they may use different word ratings for the same density or ILD.
When you are testing a mattress locally then disclosing “comfort specs” such as ILD/IFD isn’t really necessary or an important part of transparency because with careful testing your body will tell you much more about whether any specific combination of layers or components are a good “match” for you relative to the mattress “as a whole” in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) than knowing the ILD/IFD of any individual layers regardless of what the actual numbers or word ratings may be. In other words … I would consider ILD/IFD information to be a legitimate part of what many manufacturers consider to be “proprietary” information.
Many brick and mortar stores that sell component latex mattresses are also well aware that many of their customers may just be “showrooming” their mattresses and may be intending to purchase a similar mattress or combinations of layers and components online so they would have little reason to disclose ILD/IFD information to a potential customer when it won’t help them decide which mattress would be the best “match” for them anyway.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences or to other mattresses that they are familiar with than anyone else.
While they may not all have the same opinions for many different reasons … a good online retailer or manufacturer will generally make suggestions that they honestly believe have the best chance of success based on the information you provide them when you talk to them on the phone because this is in both your own and their best interests (mattress returns are very costly for a retailer or manufacturer) but at the end of the day the only way to know for certain whether any specific mattress or combination of layers is a good match for you in terms of comfort, firmness, and PPP will be based on your own careful testing and/or your own personal experience so if you can’t test a specific mattress in person then the options you have available after a purchase to either exchange the mattress or individual layers or components or return the mattress for a refund (and any costs involved) would generally become a more important part of your personal value equation just in case (and in spite of the “best efforts” of everyone involved) a mattress you purchase doesn’t turn out as well as you hoped for.
I’m looking forward to finding out what you end up deciding.