Airtable should show each record in the Calendar view titled as the value for the primary field (which is the first field on the left in Grid Views). Is that not happening here?
You will need to make a formula field with a formula like this, which assumes you have one field reporting a {Start Date}
of some sort and a field for {Number of Days}
from which to calculate the invoice date:
DATEADD({Start Date}, {Number of Days},'days')
To have dates display that way, use another formula field with this formula: DATETIME_FORMAT({Date field},'MMM-YY')
. Note: this formula will produce a string, which Airtable cannot readily use for additional calculations. Recognize that this will output a purely aesthetic version of the original date field.