Heck, it's not me that puts the size labels on clothes!!!!
I just know what I've got in my wardrobe and the sizes range from 8 to 14 and they all fit just fine. I don't recall ever wearing anything smaller than an 8, and I still have clothes I bought in HS that I wear and my 25th reunion was last year.
I envy you staying the same size. My size has gone up & down & back up again my whole adult life. I have a friend who is 65 & she can still wear clothes she has had since her children were small. She never gets rid of anything & has some fabulous things from years past.