It is relatively common for us to be "confronted" with underbust measurements under 70, but quite often the "problem" here is that we specify bra sizes differently than is often the case in bra fitting:
Our 70s bralettes are based on an actually measured circumference of around 70cm, but the finished bralette is a lot narrower due to the elasticity of the rubber, between 8 and 11cm depending on the model (i.e. finished width 59 to 62cm). Many other labels indicate bra sizes according to the finished width of the bra, which often results in these bra sizes of 60H, 65D, etc - in our experience, the best thing to do is to measure the actual circumference directly below the breast :) it can very often be the case that you have a 65D elsewhere, but a 70M fits perfectly with us, simply because of the different size calculation :)
Of course, it also happens again and again - but rarely ;) - that a value is actually measured far below 70cm below the breast - in such a case we can of course also make a bralette specially for this width, so you can help us very much just contact us at atelier@koerbchen-wien.at!
In general, the following point is very important when it comes to bra sizes: Normally, the smaller the circumference, the higher the letter that is written next to it :) We have very often "accommodated" very tall letters in our bralettes, because of course every label uses different cuts and sizes, and especially if you have done a professional bra fitting, in our experience, the result is often quite high letters with very small numbers ;) because the circumference is calculated as -10cm, and because of the narrow circumference very large cup results. Here are a few examples that we have already used successfully in our studio: "usually" 65C - 70S for us, "usually" 60H - 70L for us, "usually" 75J - 85XL for us - just to give you a small excerpt give :)
Of course we don't want to say that the bra sizes are "wrong" elsewhere, of course they often fit very well, we just give the sizes differently, and of course our bralettes fit completely differently because they don't have underwires, so don't despair if you wear a very unusual size - it's best to just ask us, we'll be happy to advise you :D