Here, have a vast amount of information about bra sizes!
I find that my feet may be either a 38 or 39 (or a 5 1/2, or a 6, or a US 7), and some clothes fit in size n
while others might fit in size n+1
, and I have never found that Adidas shoes or Top Shop jeans fit me at all, so it also doesn't surprise me that some of my bras are different sizes than others, and that some allegedly the same size don't fit at all.
And the only time I go around telling people that their clothes aren't the right size for them, is when my boyfriend has put on weight and hasn't noticed how bad his once-favourite shirt now looks.