The TNG Technical Manual
makes it pretty clear that one of the advantages of the Galaxy Class is that a large amount of it's internal space is free for customisation according to the needs of any given mission. The implication seeming to be that, like the way the bridge modules are supposed to be easy to replace without changing the rest of the ship, the Ent-D and others of her type were moldable. New areas could be added or removed as necessary.
Obviously the production reason why we never saw Ten Forward in season one was because the set wasn't built until season two. But could this also be the in-universe reason as well? Maybe the "Section 10, Forward" area of the ship was actually something else in season one, but the Ten Forward lounge was added sometime between "The Neutral Zone" and "The Child". And, of course, Guinan explicitly says in "Yesterday's Enterprise" that she wasn't on the ship when Tasha was, and Picard greets her in "The Child" as if she's a relative newcomers to the ship (even if Picard himself
obviously knows her from way back). Could it be possible that Ten Forward simply didn't exist in season one, and Guinan basically came on-board at the same time Ten Forward was added to the ship? Is there any evidence (canon or otherwise) to this effect?