In the mud throwing scene mud can clearly be seen on Gloria's dress before Claire smears it on.
When the family is throwing mud at each other, the mud on Manny's shirt disappears and reappears between shots.
Jay says that he and Gloria met while making small talk. In Fulgencio (2013) Jay tells the story of meeting Gloria when he heard her voice in a diner and sent over piece of pie to her table - he never said their conversation was at a wedding, just that it began with small talk.