DD born 3lb 12oz. Came home at 6 1/2 weeks weighing 5lb 2oz. 00000 was fairly big on her, but she was long. There's no way she would fit into a Kmart 00000, they were enormous.
She soon got too 'tall' for her 00000 clothes so she had to go into baggy 0000 clothes at about 2 1/2 - 3 months.
She's 5 months now and between a 0000 and 000, depending on the brand. Fitting well into Target 000, but still in Kmart 0000 clothes. Huge size difference between Kmart and Target!!