Are you supposed to add 4/5 inches to your underbust find your bra size?

Anonymous
My underbust is a 28 and my bust is 33 and I've lost almost 2 stone so my underbust is smaller. Today, I got measured in two bra shops. Both times I measured 28 and 33 inches, but I was told to wear a 32C or D, so they added 4 inches to the band measurement. When I weighed a lot more and my underbust was 29/30 (wearing 30 band size), I was once told to try 34B, but it was big in the band and small in the cup. I'm confused about my bra size because I thought I should maybe go down to a 28 after my weight loss. Are you supposed to add inches to the underbust?
Are you supposed to add 4/5 inches to your underbust find your bra size?
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