The supplier recommendations take into account that the FO is diluted in bath water, just as soap is diluted in the water on your washcloth, so you do want to pay attention to the supplier info. Here's an example:
https://www.naturesgardencandles.com/lime-cilantro-fragrance-oil?
If you scroll down the center portion of the product listing for this Lime-Cilantro FO, you'll see NG suggests using this FO at 5% in bath oils, soaps and bath gels. This isn't an IRFA guideline; it's what NG thinks is a reasonable amount to use in those products.
If you look to the right of the center portion, you'll see a link to the IRFA recommendations for this FO. If you click on that link and scroll down to the bottom, you'll learn Category 9 is for "...Bar soap, bath gels, foams, mousses, salts, oils &
other products added to bathwater, body washes, conditioner (rinse off), face cleansers, liquid soap, shampoo of all types, shaving creams of all types, aerosol air freshener sprays..."
The IRFA Cat 9 limit for this FO also happens to be 5%. Sometimes the IRFA is higher than NG's suggested usage -- the IRFA for some FOs is as high as 100% -- but it doesn't make sense to make a product like soap or milk bath that's 100% fragrance. For situations like this, NG's suggestions make more sense than blindly following the IRFA limits.