All services are currently suspended on the line after cracks were found on a number of Spanish-made CAF trams using the network last week.
It was believed that damage was first spotted during routine inspections in June, when services were initially suspended.
However, it has now emerged that a tram was taken out of service in December 2019 after cracks were found, before being repaired and returned to the network.
The revelation came in a private meeting held by the West Midlands Combined Authority (WMCA).
It was also revealed that seven trams are now ready to return to service having been repaired, although transport bosses say a bare minimum of nine out of the full fleet of 21 trams are required for the network to reopen.
Councillors sitting on the WMCA are desperate to get services running on the line ahead of the Christmas rush.
Councillor Ian Brookfield, the WMCA's portfolio holder for economy and innovation, said a "full and frank" discussion had taken place with West Midlands Mayor Andy Street and transport bosses over how to get the Metro running "as quickly as humanly possible".
"Many leaders, including myself, have urged all those involved to do their absolute level best to try and get a service – even a reduced one – running before Christmas," he said.
"We can't afford to lose that Christmas business. We have been reassured that all efforts are being made to achieve this."
Metro bosses have not ruled out the possibility of the suspension running beyond Christmas, with a full service not set to return until January at the earliest.
In the New Year eight brand new trams – which are currently going through calibration and testing – are expected to go into service, bolstering the fleet to 29.
At the same time the Wolverhampton and Edgbaston extensions are set to open.
The WMCA has announced it is bringing in an independent expert to assess the governance of the West Midlands Metro, while the current issues with trams are being examined by the national rail authority.