The Mishna Berura (489 sk 22) posits that if you don't say the number of weeks (on a night where there are weeks to count) in response to a friend then you may continue to count with a bracha later that night.
This is a combination of a number of considerations. First, there is a machloket if the weeks count is an absolute requirement (l'ikuva) on every day, or only on the full weeks (days 7, 14, 21 etc.). There is also a machloket if one needs to intend to fulfill the mitzva in order to fulfill the mitzva. The Mishna Berura rules that even if we think like the opinion who holds that weeks are not integral on the middle days, one still may have had to intend to fulfill the mitzva. Thus if one answered only the days and did not intend to fulfill the mitzva, he may continue and say a bracha that night.
He finally notes that for us, who always count with the weeks in a very set nussach, the very fact that someone left out the weeks shows that he was not intending to fulfill the mitzva, and can possibly even function as 'negative kavana' guaranteeing the permissiblity of continuing to recite a blessing later that night.