I don't know what they refer to on your doll specifically, but in the past I've asked AG Customer Service the same question about other dolls.

The answer I received was they mean nothing — at least they shouldn't mean anything to customers. Supposedly they are just lot numbers meant for internal usage at AG.

Confusing things further, AG not only changed the numbering system at some point after they the took over from Pleasant Company, but they also acquired a huge supply of heads marked "Pleasant Company" which they are still using.

In other words, it's possible to have a doll marked Pleasant Company #148/16 on its neck, but tagged with an AG label.

Although it was my understanding when I started to collect AG dolls, that original, early historical Pleasant Company dolls (like Addy) were more valuable, AG discounted that, offering the explanation above. e.g., While I was concerned that a doll marked Pleasant Company I had sent to the AG hospital (for repair of some problem I can no longer recall), they explained that the hospital shelves are lined with replacement heads with both types of labels. The head they choose for a particular order is just a matter of chance and (from their perspective) does not affect its value either way..

On the other hand, I've also heard that the way to differentiate an early doll representing a specific character from a later one of the same type, is by the difference in their bodies. But even after having another collector show me one of each type of doll side-by-side I could see that the earlier ones were a slightly heavier build, but I still have trouble knowing which one I'm looking at if I don't have another doll for comparison.

Still, even though the marking may not always identify the doll, if someone else has listed the same character with the identical numbers, it may lead to the information you are looking for.

In this case you may be in luck!

I tried Googling, too. here is the description I found in the first link that showed up:

"This is a 1994 Pleasant Company 18" American Girl Addy Doll Mint in her Original Box. She is a beautiful doll! Addy was introduced to the American Girl Collection in 1993 and this doll was purchased by the original owner shortly after that. The previous owner was an elderly woman who kept Addy in her original box, so this doll was never played with. Addy's dress tag reads 1994 and the tag says Made in China For/ Pleasant Company/ C1993 Pleasant Company Inc. She is crisp and clean and fresh smelling. Addy still has her original hairnet around her head, all her joints are tight and she is super crisp and clean. Addy is marked to the back of her neck PLEASANT COMPANY/ 148/16. She wears her mint cinnamon pink dress, straw bonnet with blue calico, pantaloons, black socks and shoes and cowrie shell necklace.Addy comes in her white embossed American Girl logo box in very good condition. The previous owner wrote the date of purchase on the bottom in one corner. She is such a lovely doll!!"

It is currently offered as a BIN sale for $195.00 and was either update or relisted on 10-14-09. (Item #: 130334183724)