While true, it is also irrelevant. All known antibiotics belong to a very small number of classes by their mode of action. Resistance genes often confers resistance to not just one antibiotic, but an entire class, for example mecA in MRSA. Therefore it is possible for a bacterium to develop resistance to all therapeutic antibiotics without ever having encountered the exact types.

What's more alarming is that bacteria frequently exchange genetic material between species. Just because the resistance genes have not been discovered in a pathogen does not mean that the gene cannot be easily and instantly transferred from another species, and the chance of that happening is greatly increased if the environment is flooded with resistance genes due to selection by human use of antibiotics.