Compare the weather conditions
Was the first leak during wind from one direction and the second during steady rain? Did the mark return immediately, or only after several hours? Those details can show if the same route is involved.
A repair can be technically sound while another defect nearby continues to admit water.
Old plaster can stay wet
Ceilings, insulation and timber do not dry instantly. A stain can darken for a while after the roof is repaired, particularly if materials were saturated.
Fresh dripping or expanding wetness during new rain is different. Mark the edge of the stain lightly in pencil and photograph it so changes are easier to judge.
Ask what was actually repaired
An invoice saying 'roof repair' is less useful than a note saying which slate, flashing or joint was repaired. Photographs help.
If the contractor returns, show them when the leak appeared and whether its position changed. Repeating the same patch without checking the surrounding route is unlikely to help.
Widen the inspection carefully
Once an obvious defect has been corrected, inspect uphill and sideways from the damp area. Chimney sides, valleys, roof windows and wall junctions can create overlapping symptoms.
Do not jump straight from one failed patch to a complete new roof. The next step is a better diagnosis.