The indexer is using 1871 as the year for this batch. The only date I can find is "last ****'d" 1870. What is the correct year for this batch?
I am going to amend my answer. After looking at the instructions further, there is an example of how to index a record without column headers. On that example they show to index four digits as the year, even though we don't know for sure that is a year or if it also means assessed. So, the indexers may be correct to use 1870 as the Year. But, they wouldn't use 1871, since that would be a calculation.
I think they got the date by calculating from the column that says "Assessed 1870 page". I don't believe this is the correct thing to do since we have no way of knowing what that column header means. Where I live our assessments are made every 5 years. So, if something was assessed in 1870, in my world, that date could mean these tax records could be anytime between 1870 and 1875.
We don't calculate dates anyway. The field help says:
If only a 2-digit number was recorded, you can sometimes determine the first 2 digits of the 4-digit year from other information, such as the project dates or other contextual information on the image.
That doesn't mean that you can use contextual information to make up a date.