^^^ agree with the above.
However, there is one major violation of seniority and that is when it comes to new equipment in an existing base.
As SLC and PDX got the 175 existing CRJ pilots were bypassed for transition in order to protect the operation. In some cases they flew the CRJ (or Bro) to the last day and didn’t have a spot on the new equipment - and got displaced.
“That’s how we have always done it”
TFAYD