That's not how it seemed in 94, just listen to a Zahn interview about it.
Considering they released three-novels in a 23-month period, I'd say Zahn is misremembering. Book one was released in June 1992 while book two was released in June of '93, meaning that book two had already been green-lighted before the first book was released. The dates for release can be found on Wookiepedia.
Doesn't sound like the publisher had any doubts about the books being successful.