If the informal review is done but not lowered to where a person truly believes it should be and the person goes to grievance day and loses, will the
assessment go back up to the "pre" informal review amount or stay at the amount the assessor "agreed" to and listed on the tentative tax roll for 2018.

         Yes, the assessed value listed on the tentative role is the number unless the Board of Assessment Review changes it on Grievance Day.  Historically, the BAR doesn't change them in Rotterdam unless there is a political connection.  Sorry, that's how they operate.  You would have better luck going to Grievance Day and then Small Claims Court, although that is cumbersome and has to be filed correctly.

So the amount listed on the tentative roll which was lowered a slight amount can't go back to the higher amount if greivance day is a bust?

Quoted from rpforpres

So the amount listed on the tentative roll which was lowered a slight amount can't go back to the higher amount if greivance day is a bust?

The tentative roll  values become the final values unless lowered at Grievance Day, so you are correct.  It can only get lowered, or kept the same, but cannot get raised.

Thank you Now getting ready for Grievance Day here in Schenectady for my own property here.  Then over to Rotterdam Town Hall for my son's
grievance.