“Think it through, Lyanna and Robert could have coupled before the abduction.”
They didn’t, but even if we assume they could have, the war lasted over a year, and the abduction was right at the beginning of the war. So there is no way any progeny of a coupling before the war would be a newborn baby at the end of the war. Never heard of a 12 month pregnancy even in Westeros.
Books or TV series? Remember they split storylines.