Religious records sometimes state that bride and groom got married and completed the veiling ceremony (se casaron y velaron). But sometimes they only report the wedding, recording the veiling ceremony on a different day.
In order to understand this, first we have to understand the Catholic marriage sacrament. In the Catholic sacrament of marriage one man and one woman (both free to marry) willingly and knowingly enter into a covenant for the whole life. The spouses, as ministers of grace, confer upon each other the sacrament of matrimony, expressing their consent before the church (desposorio).
This is the first part of the sacrament, but to be completed, it requires a “Nuptial Mass” with the attendance of a priest to say the prayers that give the blessing to the married pair; and the consecration of the bride to the estate of marriage (“velatio nuptialis” in Latin).
Nowadays the Catholic marriage still includes all the same components, and they are all completed during the wedding ceremony; but the tradition was different prior to the Second Vatican Council (mid XX century). As the marriage blessing was considered a celebration, it was not allowed during Advent and Lent (that are considered penance periods). Therefore, if the marriage (desposorio) was celebrated during these periods, a separate veiling ceremony (velación) was required to complete the marriage sacrament. That explains why sometimes marriage and veiling happened during the same day and sometimes on different dates.
During the veiling ceremony a red veil (pallium) covered the bride’s head, but also the groom’s shoulder, and over the veil the priest placed a white "iugale" (a kind of stole). Mixing the two red and white colors represented the indissoluble union between men and woman.
Priests registered Veiling ceremonies in separate parish books. The actual marriage date for that couple is veiling ceremony date, not the marriage, as the veiling completes the reception of the sacrament and groom and bride can live together.