Must I repeat the prayers I performed after a short discharge of blood, not the usual menstrual blood, which I thought was istihada, and then my usual menses was delayed thereafter?

The more cautious approach for you is to repeat the prayers of the days you performed without ghusl after bleeding resumed following 13 or 14 days of purity from your menstrual period. This is because the well-known opinion among the Hanbalis is that the minimum period of purity (tuhur) is thirteen days. Their evidence for this is the ruling of Qadi Shuraih to that effect, which was affirmed by Ali (may Allah be pleased with him). There are other opinions among the Malikis, Shafi'is, and Hanafis regarding the minimum period of purity. However, the opinion that the minimum purity period is thirteen days means that both red blood and yellowish/brownish discharge are considered menstruation.