The lady I purchased my littlest one from has had some that size and smaller grown. She's been a breeder for years and sometimes, they just don't grow very big and places the tiniest ones in special homes who know how to deal with that size.
Like others have said, at 7 months she's not done growing. My baby was about 1 lb 6 oz at 5 months, the smaller ones do grow and gain more slowly and it takes a few years till they're finished. There's the tiniest maltese cutie I've seen on a site, I'm in love with this baby:
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