In The Wedding: Part 2 (1998), Raymond meets Debra's priest Father Hubley, in a flashback episode featuring Ray and Debra's wedding. However, throughout the rest of the series, Father Hubley is portrayed as the Barone family's priest. This portrayal includes The First Time (2002) during which Marie brings Father Hubley to Debra's house long before the wedding.
In one of the episodes, Raymond is talking to Debra. If you look at Ray's shirt, it is clean. Next shot, it is dirty. It keeps doing this.
Robert is said to be an NYPD Officer. However, throughout the series he's shown patrolling his hometown of Lynbrook, which is a separate town and has it's own police department. Also, working for New York City he would be required to live within city limits.
In one particular episode, one of the actors accidentally refers to Doug Heffernan (of King of Queens, as played by Kevin James) as "Kevin" - his real life name. Kevin James appeared 9 times in "Everybody Loves Raymond." In the first six appearances, during seasons one and two, his character was simply referred to as "Kevin." In the final three appearances, during season three, he portrayed his "Doug Heffernan" character from "The King of Queens." This is probably because the final appearance as "Kevin" took place in May of 1998, while "The King of Queens" did not debut until September of 1998.
Throughout the series, the missing section of the large door frame between the Barones' living room and kitchen is sometimes briefly evident in the top of the screen.
In the episode with Raymond's diary, Marie makes like she is reading from Raymond's diary, however from the angle that she's holding it, it's obvious that there's no writing on the page except for a standard header on every page. Raymond also doesn't write anything when she asks him to amend the entry.
Robert and Ray are in the living room talking. When the camera faces to the kitchen, you can see a crew person standing just outside the window.
The front door on both houses face the same direction. If they lived across the street from each other, their doors would be face to face. Marie's kitchen door would actually be facing Ray's house.