The report said staff were "learning" a new software system ahead of parish, district and parliamentary elections in Oxfordshire on 7 May.
Details for about 200 overseas voters had not been sent to the printers. Alternative votes were later issued.
Returning officer for South Oxfordshire and Vale of White Horse district councils released the interim report.
David Buckle said staff were "learning as they went along".
The same number of postal votes had not been sent out in the Oxford West and Abingdon constituency, the report said.
It said there was no system in place to confirm the relevant information had been received from Oxford City Council.
In both cases alternative postal votes or proxy votes were offered and a large proportion of people took these up.
A large fire at the Crowmarsh offices in January caused a "significant amount of disruption" as paper records were lost and the computer system was down for almost two weeks.
Jeremy Thomas, returning officer for Oxford City Council said: "The problem was an isolated one and as Vale of White Horse District Council acknowledge there should have been systems in place to check the data being received."
Adopting a new computer system led to postal votes not being sent out ahead of the election, a report has found.